Alright, here's what happened a few weeks after my SIL moved in with us. My wife and I'd been going at it like rabbits. Our libido was through the roof. On her part she said it was just because I was always horny and couldn't keep my hands off her. She attributed it to her new wardrobe and she's right on that. But also on my part of course I was enjoying the delights of my wife's new clothes AND I was also enjoying the unlimited SIL used panties and half-nakedness around the house perk.

Saturday morning in the kitchen, wife's on her period and crabby as can be. My SIL had developed this routine to pull on my wife's pants to see what panties she was wearing and then running off to her room to put on the same pair if she also had it. She'd the come back and bump het butt against my wife whilst happily shouting "twinkies! twinkies! twinkies!" and it usually ended with my wife just brushing her off. However, this time she shouted at her little sister "Stop that! God you can be such a child sometimes!" I could see my SIL's eyebrows drop and her face change to sadness. My wife quickly reached out to her, hand on her shoulder "I'm sorry sis... wanna go get a pedi? I could really use one." with that my SIL's face brightened up again and she celebrated with air fist pumps around the kitchen. Then she comes to me pointing at my face "Suck it bitch! It's girl time today!" and my wife immediatelly reprimanded her "Show some respect will you!? You are a guest and he is my husband!" With that my SIL apologized but on her way down the hallway signaled me to 'suck it' while silently laughing. They get their things and off they go to get a pedi.

When they pulled out of the driveway I immediately thought about going into SIL's hamper but decided to wait a little. Instead of waiting patiently doing nothing I did a few things around the house and then checked Snapchat and sure enough after some 30 minutes they both had posted about getting a pedi. That was my queue. I stripped completely and ran to her room. By then I had developed my hamper raid routine taking out all her clothes and laying them in order so I would know what to put back in what order. The fresh pair from the morning before she changed was a red no-show laser-cut cheeky from PINK. It was perfectly crusted from her pussy. As always, inhaling her aroma into my nostrils got my blood pumping to an immediate erection. I gathered her other panties and began to rub myself with them all. The fresh red panties felt so good I had to try them on. Then I laid on the bed on my stomach and continued to sniff the rest of her panties. Instead of jerking off I began to just hump the corner of her mattress. It felt really good, but I needed more so I got a couple of her bras and messed around putting them on my crotch until I found a really good position and continued to hump away. Her panties on my face, wearing a pair, humping into her bras, it was all so erotic and forbidden that I quickly reached my point of no return. I picked up the pace and began to moan her name out loud until I came all over making a mess with cum spewing out of the red panties onto the other ones and onto the bras and onto the comforter. Right away PNC set in and I and began to panic realizing what I'd done. I ran to the kitchen, still wearing her red panties, in search of paper towels to try and clean up the mess. Went back to the room and began to clean what I could. I was too afraid they'd come back soon that I just threw everything back in the hamper and ran off the house to wash the truck.

They came home over an hour later. My wife said they should have just gone to the grocery store from the pedi and said she'd go back out grocery shopping after using the restroom so she went to do her business. Soon my wife came back and asked my SIL to accompany her to which she responded "no thanks, I need to wash and get ready. I'm going out later" Then my wife turned to me as I was freaking out internally over my SIL's need to do laundry knowing what I'd done earlier "will go you with me babe?" I just nodded and headed out with her. On our way out she asked "you washed the truck didn't you?" I confirmed. She reached over to me and took my keys and handed me her car keys "I'll take care of groceries, you take care of my car. It needs a good wash!" We kissed and went our separate ways following my new assignment. I came back home in 20 minutes. To my surprise it was very quiet in the house. I walked past my SIL's room and noticed she was laying face down on her belly on the bed, headphones on and watching something on her phone. Didn't think much about it but did stare a little as her ass was devouring her shorts. I decided to head back to the living room and just sat there thinking about turning on the tv when I heard a soft moan. I quietly made my way back to her room and noticed she was still in the same position but with her hand down her shorts and I could now see she was watching porn - probably thinking my wife and I would be a while at the grocery store.

The sight of my SIL masturbating made me drop my pants in record time. I was jerking off before I knew it but I was also scared out of my mind. I was desperately trying to not even breathe as to not make any noise. But of course beating my meat was not a quiet affair so I went back to the living room. After some minutes I heard noise coming from her room and I tippy-toed my way over again without peeking in this time. I heard her "fuck yeah! give me that big dick!" and OMG when I did peek in I saw she had a hair brush handle in her pussy! I didn't want to push my luck so I didn't peek in again. Instead I just listened as she continued "yeah! fuck me hard with that big dick! yeah! pound my pussy!" She went on until she came hard on that hair brush handle. I moved back like a ninja on may way to the living room again. I was so exited about what I'd just witnessed that I kept hearing her voice in my head over and over telling her hair brush to fuck her hard.

She did not come out of the room for a while so I walked passed it as if just getting home and waved at her sitting on the side of the bed taking her clothes out the hamper and she looked at me "hey back already?" and I responded "just me, your sis went to the store by herself. Sent me to wash the car instead." My SIL looked at me confused and a little embarrassed "so you just got back or you've been back a while?" and I calmed her down "a bit ago but just a few minutes" She was suspicious but didn't continue that thread. Instead she turned to her clothes "man I really need to wash, even the comforter" she looked at me "what a big load..." I just stared at her but she picked up the clothes and just walked out to go wash with no further comments. I went back to the couch.

SIL came back and sat on the couch next to me as I watched tv. She made a point to show me her toes and put her feet on my legs to make sure I got a good look "cute, right? Sis wanted to get boring pedis but I told her she needs some white-tip action on her toes. Makes things sexier..." she said as she wiggled her toes on my leg and continued "don't you think?" I just said "yeah, definitely sexy looking toes" as she smiled on my compliment. Then she turned back to the clothes "that was a huge load I had to take care of" I replied "no worries, the washer can take it" almost choking on my words. Then she started talking about her plans for the night and the guy she was seeing. I asked for details and she said "just some guy. I don't expect much but..." and she bit her lip "I'd be happy if he's at least 7 inches though." I challenged her laughing "do you even know what 7 inches is?" She very sure of herself showed me with her hands and I burst out laughing "not even close!" and she came back "oh yeah, prove it then!" I ran to the garage to get my measuring tape and on the trip to and back began to wonder about the dicks she's actually fucked. When I returned I inquired about it. She said she'd just show me but I didn't want her to cheat so I told her to close her eyes. She complied and said "ok but put it here so I can measure better" as she tapped her forearm. I placed the measuring tape on her forearm and began to pull it out. Told her to stop when she thought I was 7 inches. She was at about 11 inches and opened her eyes "what the fuck!? Ok I was way off there." I smirked over my victory "see, told you. Girls don't even know about sizes like that" and she got offended but I wanted to turn things around "so what's the biggest guy you've fucked?" I asked. She said "Ok let's measure again" as she closed her eyes. Then she began to sort of stroke her forearm in an attempt to remember "here. that's how big he was" Then she opened her eyes and gasped "fuck! no wonder he nearly split me in half" She was at the 9 inch mark. I wanted to know more "so how big was your first boyfriend? the one with the perfect dick?" She closed her eyes again and again began to stroke her forearm "here! I know this one for sure!" opened her eyes and saw the 7.5 inch mark and continued "well damn I guess I'm a 7.5 then!" as she let out a big laugh. Curiosity got the best of me "so... you think you and your sis are the same size? You do have very similar bodies" I asked laughing and blushing. She just got serious "oh BIL you don't have to worry about that. Your 5 inches are the perfect size for her!" I was floored. She noticed my reaction and reached over "oh, it's ok. We're girls, we talk about stuff and 5 inches is average so you're good!" and she gave me a thumbs up and hopped off the couch "ok, gotta go get ready."

I sat there for a while just thinking and wondering. Could my wife take 7.5 inches? Would she enjoy the size difference? I couldn't stop thinking about it and eventually ordered a 6 inch dildo from Amazon with over night delivery. It was all good and I was looking forward to receiving it and examining it to make up my mind about it. However, things didn't go as planned. The next morning I was in the shower and the day seemed normal. However, when I went to the kitchen both my wife and SIL just starred at me. My wife began "I grabbed your phone to order something from Amazon...." I knew what was coming next but tried not to panic. She continued "and I... well.." she paused and my SIL came running at me with the box laughing her guts out "WE TOTALLY KNOW WHAT'S IN THE BOX!" she shoved it on my chest and ran to her room laughing. My wife stood there red as a tomato just starring at me, not mad but just embarrassed as can be. I had no words. She broke the silence "well.. are you gonna put that thing away or what!? or were you planning on having it here in the kitchen as a display?" I ran to the room to unbox and unpack and stayed in the room for a while hiding from my embarrassment. When I went to the kitchen they were both there again. My wife was still blushing and my SIL just smiled as she looked at me "you dirty dirty boy!" and my wife thankfully defended me "oh shut it sis. Our business is non of your business." We had a very awkward and mostly silent breakfast that morning.