Back when I still lived with my parents, before I left for university, I had a best friend called Harmony. Actually she's still a close friend now, even if these days we don't get to see each other very often and mostly just talk online or by text.

Harmony and I had been friends for years, so there was nothing surprising about her sleeping over at my house after a night out, or her sharing my bed. After all we'd done it plenty of times before, just as I'd shared her bed more times than I could count.

This time though, something happened that changed things between us. I woke up early and realised that in my sleep I had curled myself around her as she lay on her back, and one of my hands was resting on her breast. I know I should have taken my hand away and rolled over, but I didn't.

Honestly I was just curious. Her breasts were much smaller than mine, and she felt so different. Where I was soft, hers was firm. Where mine were rounded, hers were more conical. I closed my eyes and gently squeezed and stroked her through the thin t-shirt she wore to bed. I had some half-formed idea that if she woke up and said anything, I could pretend that I was asleep.

As I kept exploring with my fingertips, I brushed across her nipple and was surprised that it was hard. I never knew that could happen while you sleep. Actually, I hadn't even given it a thought before then. While that idea percolated through my head my fingers took on a life of their own, tracing light, tight circles around her nipple.

I noticed a change in Harmony's breathing, faster and shallower. I opened my eyes, and she was wide awake and looking straight at me!

I snatched my hand away as if it was burnt and tried to stutter out an excuse through my embarrassment. Harmony interrupted before I could even form a coherent sentence "Aw why did you stop? I was enjoying that!" Then she giggled.

Her reaction confused me. At the time, she had a boyfriend, and as far as I knew neither of us were into other girls, so how could she have been enjoying it? Harmony didn't give me time to process anything. She quickly sat up in bed, pulled her t-shirt off over her head, and just as quickly laid back down again, with the duvet cover pulled down to expose her small breasts.

Harmony looked at me expectantly. When I didn't react, she giggled again. "Now you have to take your top off, silly!"

I was feeling out of my depth. This was Harmony after all, not some boy I'd let pick me up. I knew where I was with them. Nonetheless I did as she suggested and lay back down, feeling self conscious. I told myself that my nipples were hard because of the cold air - why else would that happen? - but as I lay staring at the ceiling I could feel her eyes on me.

I resisted the urge for a few seconds, then looked across at Harmony. I was right, her gaze was locked on my breasts, and she was gently biting her lower lip.

Out of the corner of my eye I noticed something moving. I turned my head to look properly. About halfway down the bed, the duvet was rising and falling in a slow, steady rhythm. I must have watched for five or six seconds before I realised what I was seeing. Harmony was masturbating. In my bed. While I lay next to her, topless.

I looked back to her face and we made eye contact. Harmony was still biting her lip, with a look of intense concentration on her face. She nodded once, then her eyes fell back to my chest. I should have been shocked. I should have told her to stop. I wasn't and I didn't.

As I saw the first beads of perspiration appear on her forehead, my hand stole down under the duvet and into my panties. I'd already felt myself getting wet, but until my fingers touched my slick clit, I hadn't realised just how wet. Harmony smiled and nodded again as I started rubbing myself.

The duvet stopped me seeing what she was doing, but I knew. I could feel when she sped up and slowed down, I could hear the sounds of her wetness as she switched to thrusting with her fingers, the soft gasps of pleasure which slipped from her lips.

I matched myself to her, rubbing when she rubbed, fingering when she did, moaning softly as I gave myself over to the sensation. I felt Harmony orgasm. Felt her hips rise to meet her fingers, her body trembling uncontrollably with her release.

I felt a moment of irrational disappointment that she had finished before me, but I didn't stop. I sent my other hand down between my thighs, rubbing my clit as I thrust into myself with two fingers. Close. Closer...

Harmony pressed her lips to my nipple. She didn't suck, but that one small unexpected kiss sent me flying over the edge. As the orgasm raced through me, I made a desperate attempt to muffle my moans, even biting into my pillow to avoid waking my parents as they slept in the room next door.

Afterwards we lay panting side by side in my bed, neither of us speaking. I felt Harmony's hand reaching across to me and entwined my fingers in hers.

"You're such a bad girl" she said with a giggle in her voice.

"Me?" I answered in mock outrage. "You started it!"

Harmony didn't say a word. She just gave me 'the look'. I kept a straight face as long as I could before we both dissolved into fits of giggles. She prodded me in the side with her finger, I retaliated and before long it descended into a full-blown tickle fight, which ended with me kneeling astride her waist and pinning her arms out to the sides.

I think we realised at the same time that this position left my breasts dangling enticingly above her lips. Harmony gave me a wicked grin just as I half-whispered "Don't you dare"!

She did dare. Her tongue slid out from between her lips and before I could lean back out of reach she licked across my nipple. I won't lie, it felt good, but part of me also felt that it was wrong, that I shouldn't enjoy it. I sat up, keeping her wrists pinned as I tried to work through the conflicting emotions.

Harmony squirmed beneath me and I had to lean forward to keep holding her down. This time, I was ready for her though. As she lifted her head and poked her tongue out, I moved back just far enough that she couldn't quite reach, no matter how hard she stretched. Strangely, I found that even more exciting than when she had actually licked me, watching the tip of her tongue searching for my nipple but never making contact.

It became a game for me, leaning forward to give her hope, then pulling back again. I got daring, moving my breasts closer to her lips, waiting to the last possible moment before taking them away again.

She tricked me. Harmony looked to the side, acting as if she was bored of this game and when I leant in again so my breast almost brushed her cheek, she lunged. This time she didn't just lick me. Her whole mouth engulfed my breast and I felt her teeth clamping around my nipple. Not enough to hurt, but I knew better than to pull away.

She alternated between sucking and swiping her tongue across my sensitive skin. It felt so good that my earlier doubts were washed clean from my mind. I never wanted her to stop. I'd let a few boys grope me under my shirt, but nothing could have prepared me for how good this felt.

I released her wrists, forgetting why I was even holding them and placed my hands on her breasts, using my fingers to emulate her lips and tongue. When she sucked, I pinched her nipples, when she licked, I would stroke. We got so caught up in the moment, we didn't realise how loud we were getting, moaning and giggling.

There was a knock on my bedroom door, followed by my mother's voice "Are you two OK in there?"

We broke apart and dived back under the duvet, both still laughing. "Yes Mum" I replied. "We were just play fighting"

"Ok then, just keep the noise down. Your dad is still sleeping. I'll get breakfast on"

Harmony and I exchanged a smile. As though my mother's intervention was a signal, we both knew our little playtime was over, and we got out of bed and hurriedly got dressed to go downstairs. There would be plenty of other opportunities after all...