This story is a continuation of a mini-series I wrote last month. Earlier parts are available in my profile -- this chapter will make a lot more sense if you read those first:

Part 1: Thin Walls

Part 2: Say Please

Part 3: Hard Work

Part 4: Starry Nights

Themes: reluctance (maybe some non-con/dubcon and blackmail), lots of teasing, mostly-unintentional edging/denial, premature ejaculation, and cheating.

Characters in this story, as in all of my stories, are 18 . It's a work of fiction. I welcome feedback, and my entire archive of stories is always available in the stickied post in my profile.

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The more I thought about what had been happening, the more irritated I got. Enough was enough, I decided, when I woke up the next morning. I had to talk to Summer. And I needed to do it soon.

In mulling it over last night, one thing had become clear to me. Trying to deal with Summer after I had been teased beyond belief was a losing proposition. I couldn't handle it.

It was embarrassing to admit it, but it was true. If I tried to talk to her alone tonight -- or tomorrow, or another moment when an easy opportunity presented itself -- I knew how it would go. It would be after hours of teasing. She would've been sunbathing by the pool in her bikini. She would've already interrupted Jessica giving me a blowjob, maybe, or found a way to tease me with her body while we were playing charades. Or something. Probably a few of those, really. She'd spend another day making sure I was helplessly turned on, and the outcome would be predictable: I wouldn't be able to resist her, I'd cum for her again, and suddenly I'd "owe" her three, or four, or seven orgasms instead of two.

Ugh, even the way she talked about it was infuriating. That I owed her two orgasms. Like she hadn't been the one teasing me all day long, setting me up to not be able to last.

She was doing all of this. I needed to find a moment to talk to her about it. A moment when I was feeling in control of my own libido, could actually have a rational conversation with her. A moment when I wasn't dazed and guilty from an embarrassingly quick orgasm.

My face flushed, just thinking about it.

"You okay, babe?" Jessica glanced over at me. We were eating breakfast at their kitchen table.

I nodded. "Yeah, I uh...just...didn't sleep well..." I mumbled the words.

"Yeah, you don't look so good, tiger. Did you go a little too hard last night?" Summer was there too. Of course. Her voice had its usual teasing playfulness to it. I glanced over at her. She was wearing her pajamas, and I could see most of a full, smooth pale breast peeking out from the side of her tank top.

God, everything about her was fucking hot. That smirking tone in her voice. The way she looked up at me, her eyes knowing. That sexy body.

I could feel my own body reacting. Yep, the sooner I talked to her, the better.

"Well, my parents said they were going to do a grocery run today," Jessica said, earnestly. "We could go with them, grab you some cold meds and stuff if that'd help."

I jumped on the opportunity. "I, uh, think I might just stay here, try to get some more sleep. But if you don't mind picking some stuff up, I'd appreciate it."

Jessica nodded, the picture of concern. "Summer? You want to come?"

Summer's eyes were on me. Still knowing, but calculating, now. "Nah," she said slowly. "Sounds kinda boring. You should get some more beer, though; we're almost out." She yawned, stretching lazily. The tank top rode up, revealing just a hint of smooth skin at her stomach.

Jessica rolled her eyes. "Suit yourself, sis. Well, babe, feel better." She patted me on the shoulder as I stood up and headed back to our room.

I hadn't slept especially well, but I felt clear-headed, in control of myself for a change, as I lay listening to Jessica and her parents gather their things and head out.

Time to tell Summer I was done cheating on my girlfriend. That this was a fucked up thing for her to do to her sister. To put a stop to all of this.

There was only one problem.

Summer didn't seem to want to talk.

I emerged from my room as soon as I heard the car leave the driveway, ready to go to war...but she was nowhere to be found. I glanced out back and out by the pool, but didn't see her.

In the end, I realized she had probably just gone into her room.

I hung out in the living room, scrolling on my phone using the cabin's shitty wifi, prepared to wait her out...but she showed no signs of emerging. Ten minutes went by. Then twenty. Then thirty. Then forty-five.

It was a long trip to the grocery store -- the cabin really was middle-of-nowhere -- but eventually I started to feel antsy. I needed to talk to her now. I wasn't sure how long it would take. I absolutely did not want Jessica coming back in the middle of this conversation.

Feeling a little like I was approaching a dragon's lair, I stepped up to the door, took a deep breath and knocked.

"Took you long enough. C'mon in, Jason," she called. Her voice was teasing, confident.

She was infuriating. Blushing a little, I opened the door, stepping into Summer's room.

I hadn't seen it until now, I realized. It was a little bigger than the room Jessica and I were in -- Summer had gotten there first and, of course, had taken the better room. Bigger windows, better light.

Summer was in bed. The blanket was pulled up under her arms, but I could see -- from her bare shoulders -- that she was probably naked. Or at least topless.

It felt like another ploy to keep me off-balance, aroused, so I tried to ignore it. "Hey, we need to talk."

She nodded. "Yeah, we do. Why don't you have a seat?"

The only place for me to sit was on the bed. With her. I shook my head. "I'll stand."

"Suit yourself." She shrugged. "So...what did you want to talk about?" She adjusted the pillows behind her so she was sitting up a little bit more. The blanket fell forward a little, showing off more pale chest, the full curve of the top of one breast. I tried not to notice.

"Look, uh..." I ran a hand through my hair. "Enough's enough, Summer. I'm not going to keep doing this. It's fucked up. What's been happening is done."

She nodded. "Okay. I mean, I told you a few days ago that I didn't want to do anything you don't want to do."

As easy as that? I felt a flare of anger. "Y-you've been horrible to your sister," I spluttered.

She scoffed. "I've been horrible to her? Does telling yourself that make you feel better?"

"You've been...you're...seducing me," I blurted out.

She laughed, then. It was an easy, knowing laugh. "Guys always say stuff like that. You showed up here and make sure to brush against me on your way into the cabin. You sat in between me and your sister under the blanket, right up against me. You've taken every opportunity to be shirtless around me, by the pool, chopping wood...the walls in this place barely don't exist, but you've been jacking off thinking about me anyway, fantasizing about me. Last night, instead of just heading to bed when she started falling asleep, you hung out with me and stayed up after your girlfriend fell asleep to listen to me talk about another time when I masturbated for a guy. She was right there. But sure, I'm seducing you." She rolled her eyes.

"That's not what...that's..." I was suddenly on the back foot.

"Can I tell you what I think is really happening, Jason?" Her voice went soft, now. "I think that I make you realize everything you missed out on. You settled down with Jessica early in college. And she's great. Pretty, smart, loyal. Even game for some fun, sometimes."

I was speechless. Summer sat up more. The blanket was in danger of just slipping down and revealing her tits. She didn't seem to notice.

"But you're realizing that people like me were probably always out there. Fun. Playful. Sexual. Hot. Someone who enjoys titfucks, blowjobs, who likes to tease. Someone who loves...cock. Big cocks, especially." She lowered her eyes, glancing at my groin.

I realized, with a surge of embarrassment and horror, that I was hard, now. And it was certainly visible to Summer.

She met my eyes, her voice smug, now; she adjusted herself under the blanket. "And you just can't help yourself. You wanted all of that. All of this. But don't worry. I think Jessica's feeling some of the same things. She likes that I think you're hot, that her slutty little sister wants what she has. You two have been talking about me nonstop. She likes thinking about you fucking me." She smirked. "She just has it all wrong. She thinks you'd show me a thing or two, likes the idea that even though I'm so sexual, you'd make me cum all over that big dick. She doesn't realize that her stud of a boyfriend Jason just can't handle me."

"All of that is beside the point," I said, haltingly. "This has to stop."

In spite of myself, in spite of the anger I was feeling, I could feel my cock throbbing. I knew she had a point. And hearing her talk about it was so fucking hot.

She shifted again under the blanket. She was looking right in my eyes, now. "Look. You can stop doing these things with me whenever you want. But I'm not going to stop being myself. If you can't control yourself, that's a you problem."

She sounded so fucking pleased with herself. This wasn't going how at all how I had planned.

And then, mockingly, she said, "After all, that's why you owe me two. Because you can't control yourself."

Up until this moment in my life, I didn't know what the phrase seeing red meant.

But at the expression on her face, those words, the arousal I was feeling -- it all just made me mad. I was trying to do the right thing, and somehow here I was again. Alone with Summer. Turned on, with her teasing me.

All my frustration, the feeling of powerlessness, crystallized into anger. It was infuriating.

"I don't owe you anyth--" I took two frustrated, angry steps towards her without realizing it. And then froze.

As I was stepping forward, she moved slightly again, and I heard a sound. A wet, sliding sound. From underneath the blankets.

She was...getting off on this?

She gave me a sly little smile, taking in where I was looking. Her the motion under the blankets became more rhythmic, less subtle. "Ah...I was wondering when you'd...mmm...notice."

The movement, combined with the sound of her voice, stopped me in my tracks. "W-what are you doing?"

"Well...we all get off on different things, Jason." She bit her lip, obviously concentrated on the sensations from what she was doing.

"J-Jessica likes thinking about how you'd put me in my place, make me cum easily." There was a slight tremor in her voice.

She giggled. "You like your girlfriend's slutty little sister getting you off. Maybe you like thinking about getting me off...even though you haven't." My cock twitched at her words.

And I..." she let out a little moan. "I like how my sister's boyfriend can't control himself. Wants to fuck me, but feels guilty about it. Wants to put me in my place like his girlfriend says, but he gets hard so easily, cums so fast..." she let out another, louder moan.

My mouth was dry, now. I should leave. Walk away.

As if echoing my thoughts, she said, "You should probably leave...unless you want to watch." That sly little smile was back on her face again.

I should go. But I stood, frozen.

Slowly, agonizingly slowly, she pulled the blanket and sheets down her body and away.

I stared. I couldn't help it. Round, creamy tits. Her prone position just emphasized how full they were -- big against her petite frame. Round hips and ass, her thighs spread slightly...

As I watched, one hand worked a thick, black dildo in and out of her wet pussy. She let out another little moan.

Fuck. I spent the next thirty seconds or so watching her fuck herself, staring at the black length pumping in and out of her.

"I'm...getting close, Jason..." Her voice was a breathless moan, now.

Unconsciously I reached down to adjust myself. My cock was so hard in my jeans it was uncomfortable.

Summer glanced down, her eyes following my movement. "Get it out," she whispered, peremptorily. As she spoke, she continued to pump the dildo in and out of her.

Dimly, I was aware that this was bad. I could see where this was going to end up. But I couldn't say no, not with her, naked and turned on, right there in front of me, fucking herself. I unbuckled my pants and dropped them and my boxers to the floor. Fuck, I was so turned on.

"Ah...ever seen a girl use a toy like this, Jason? I don't think Jessica even owns one of these..." her voice was wanton, but mocking.

I blushed, and shook my head. She was right, I thought guiltily -- I didn't think Jessica owned any sex toys, let alone a big black dildo. Jessica had never let me watch her masturbate.

Summer was staring at my thick erection, now. "God, I've been thinking about that cock in me since the shower yesterday; this is the biggest toy I own, but...come over here..." Summer was fucking herself with it again, more aggressively now, punctuating her words with gasps each time the thick length filled her.

I should go. But the sight of her in front of me, naked and staring at my cock, was too much to resist. I stepped closer to the bed. Summer sat up, and with a whimper, pulled the dildo out of her. She held it up next to my cock.

It was a big dildo, about as thick as my cock. But I had a big dick. I was probably half an inch longer.

"Fuck." She breathed the word out, her gaze flicking between meeting mine and looking at my thick length. I hadn't seen Summer like this -- I had seen her turned on, yes, but always in control, always playing the slutty tease.

Right now, she was staring at my cock like I was the one in control. She looked up at me, and with a helpless whimper, she said, "I need it, Jason. Fuck me with that big dick."

I fought with myself. This would be different than what had happened so far. Worse.

"I'm close," she whispered. She was staring into my eyes now, watching me, like she knew exactly the battle happening in my head. "Just make me cum, and we'll call it even." There was a pleading note in her voice.

Fuck, that would be so hot. But with that thought, the guilt surged in me. This wasn't Summer sneaking into the shower after days of teasing me, or giving me a handjob under a blanket while I resisted. She was trying to get me to take the initiative, to fuck her. It was wrong. I could feel the guilt strengthening my resolve. I shouldn't be doing this.

And then her lips formed a mocking pout. "I mean, Jessica thinks the idea of you making me cum is so hot...but I guess you know you can't do it, huh. Just can't last...Poor Jason, such a nice big cock, but it just cums too quick..."

Well, that derailed me completely. I am slightly ashamed to admit that I actually let out a growl. Whatever guilt I had been feeling was overwhelmed by shame mixed with anger. Fuck Summer. My cock cums too quick? I'd show her.

In one swift motion, I stepped closer and put my hands under her thighs, grabbing her body and half-lifting, half-throwing her so that her pelvis was lined up with the edge of the bed. She made a little gasp at the sudden movement.

But I paid no attention to that. I stepped between her thighs, grabbed an ankle in each hand, and pushed her legs apart. She moaned.

"You want this big dick?" I grunted the words out, and without waiting for a reply, I lined my cock up, and slid it inside her, as far as I could go. She was wet, warmed up by the dildo, and took my full length easily.

"Oh, fuck, yes," she moaned, gaze fixed on my length sliding inside her. "Pound my little pussy," she pleaded.

And I did. I started fucking her as hard as I could, days of frustration, of trying to hold back, to do the right thing, all finally boiling over. She had been propping herself up on her elbows, but collapsed onto her back, letting me use her. "Oh my god -- yes, yes, yes," she was moaning, each word punctuated with the slap of my skin against hers as our hips met. Her big tits shimmied, bouncing with each thrust of my cock into her.

"Fuck, you feel so good, I'm such a slut for your big dick, I love it, use me, use me, use me," she was still moaning, words pouring out of her like she couldn't help it.

I grunted in reply, loving every second of it. As when we had fucked in the shower -- she felt incredible. The way she was able to take my full length, tight but somehow soft, yielding around my girth, was amazing.

There was only one problem, one nagging sensation, ruining the feeling of dominating her.

I was getting close. The thought was embarrassing, but I couldn't help it; the sensation of an impending orgasm started the moment I was fully inside her, and it got stronger and stronger with each thrust. My sex life with Jessica -- nice, demure, Jessica, who needed me to take things slow, who had always gotten off easily to my cock -- hadn't prepared me for fucking Summer, legs spread wide, obviously loving taking my cock as hard as I could give it.

I didn't show it. I didn't want Summer to know. I tried to keep up the pace, hoping she would just cum. But evidently she meant something different when she said she was getting close than I did. Before too long, she still hadn't cum yet, and I knew I only had a few more thrusts before I blew my load.

And then I only had one more thrust. I bottomed out in her, holding still, trying to give myself a beat to recover.

She let out a whine. "Don't stop, fuck me with that big dick, harder, please, I'm so close," she pleaded.

Well, I knew if I kept fucking her, I'd cum. But it didn't matter, now. I was too turned on. She was begging. I pulled almost all the way out of her, ready to finish myself with a few more hard thrusts, even if it didn't make her cum.

And then we heard the crunch of wheels on gravel, a car pulling into the driveway. I froze in shock. They were back.

Jessica was back.

"Come on, don't stop, we still have a little time, they have to unload the groceries, they'll think we're both asleep, fuck me," Summer whispered, pleadingly.

But the guilt surged back in full force. Jessica. I gathered all my willpower and pulled away, pulling out of her and starting to pull my boxers and pants back on. "N-no," I muttered.

Summer let out an annoyed whine, looking at me in disbelief. "What the fuck, Jason."

"I-I'm not going to do this to her, Summer." I felt shame that had nothing to do with how long I lasted in bed, and everything to do with being a piece-of-shit-boyfriend. I headed for the door.

Her eyes narrowed. "If you didn't want to fuck me, you shouldn't have fucked me. Not finishing me off is..." Her voice trailed off in a heated whisper, eyes glittering with frustration.

I was at the door, now, pulling it closed behind me, when she spat out one final, venomous phrase.

"I'm going to make you regret this."

My heart sank.

Uh oh.