Inappropriate [m]asturbation with my [f]riend's wife's little sister | 2016

I closed my eyes but couldn't sleep. It was very early morning and the cabin was completely silent...silent except for the most subtle, eerie sound. It was like water gently lapping against the shore, but the air was completely still. I trained my ears, wondering what it could be. It would go away for a minute, and then come back...but just barely, almost unnoticeable. I wondered if she could hear it too...my bedmate. She was the little sister of my best friend's wife, just turned 16. She had passed out hours ago and the space next to her was the only one left in the cabin. She was sleeping. Or was she? I noticed her breathing seemed measured...controlled. Then it hit me. Hard. And I knew what it was. She was masturbating. Right there. Right next to me. And knowing this, the sound became amazingly clear. I could hear the slurping, gurgling sounds of her finger slowly dipping between her lips. I listened to her incredible wetness...then heard the slightest sigh. She had been touching herself all along...for maybe 20 minutes or longer... She had been in my car on the way up. My buddy had a compact pickup loaded with gear, and she barely fit in there, so I invited her to ride up in my truck. I wasn't really looking forward to babysitting a high schooler the whole ride up, but she was friendly and we enjoyed some good conversation about school...life. She was fun, and easy to talk to. And attractive, although I tried not to think about her like that. She seemed too young to be wearing the clothes she had on...tiny little shorts and a string bikini. But, it was summer, we were on a cabin trip. She wanted to have fun, and for us to have fun, and made it clear that she was old enough to take care of herself. As soon as we unpacked she cracked a beer and smiled at me. I just shook my head. She was about 5'2" with a very tight, track-conditioned body I tried not to think about. But I was thinking about it lying there...I was thinking about her little ass, pert breasts. I was ashamed. She was over ten years younger than me. Sill, I couldn't help it. She seemed to get louder...as if she was sure I was asleep...or maybe she was lost in herself. I was hard as a rock. I decided I would just lie there...silent...and let it pass. I listened to her breathe...stimulate herself rhythmically. Her sighs were subdued, and her body struggled not to writhe. I just needed to hold out until she was done. Then I could sleep an pretend it didn't happen. The minutes passed. She wouldn't let up. She just kept at it. I could feel my heart beating, my cock throbbing as I listened to her. Finally, she seemed to lose her inhibitions and was bearing down on herself. She was stroking herself aggressively, and I was sure she would orgasm soon...but she just kept going. I couldn't stand it. I started to stroke my cock...very cautiously. She kept going strong for what seemed like forever, and then eased off to the pace she had been at earlier. This went on for probably another 20 minutes. At some point I realized she knew I was stroking myself, because she seemed to stop caring about being quiet. The sound of her pussy was almost echoing off the walls of the bedroom, and her breathing was heavy. She eased closer to me and I felt her breath on my ear. She whispered my name, then asked me to cum on her...to cum on her belly. I turned to my side and stroked as she assaulted herself. I didn't last long and emptied a huge load of hot cum all over her belly. She said "fuck yes" and convulsed in what appeared to be orgasmic bliss. She rubbed the cum all over her belly and over her breasts, then tasted it. Then she said "thank you" and went to sleep, so did I. We woke up the next morning like nothing happened. We haven't talked about it since.