Recently I was over at a friend's apartment hanging out with her and her boyfriend, and like always they ended up making out for a little while, but this time when I was there she started leading him into the bedroom. I knew what was going to happen and was planning on heading home, but she said I didn't have to go. Half jokingly she said I could jack off if I wanted, but I told her I was OK and they went into her bedroom and closed the door. At first I wasn't going to, but the more I thought about it, the hornier I got. Just thinking about them both getting naked and fucking their brains out made me hard, so I decided to go for it.
At first I just pulled up the leg of my shorts and started stroking myself but it was a little uncomfortable, so I just pulled them down and took off my shirt, leaving me completely naked on her couch while I could hear them going at it in her room. I tried matching my strokes to her moaning, but I didn't last very long. I guess it was what was going on, but I came really fast, blowing a thick white load of cum on my stomach. I went to the kitchen and wiped up with a paper towel and got dressed again before they came back out.
Later on, after he left, she asked me if I did it, and I told her I did. She laughed and apologized for leaving me like that, but she said that any time I was there I could masturbate, as long as I didn't make a mess. Next time, I may even tell her she doesn't need to leave the room.