I love this site. Reading the stories gets me so horny, so here's a contribution from me.
I recently went on a canal boating holiday with my older brother, Martin, his girlfriend and my best friend, John. Obviously Martin and Jenny shared a cabin and John and me shared one. We had adjacent beds with an aisle in between from the doorway. It was very hot and we kept the door open at night to let in some air. It opened inwards against my bed so that John couldn't see my face and chest.
On the second night after John and I had talked a bit we both settled down to sleep. It was then that I could hear my brother and Jenny getting horny as the walls on the small boat were quite thin. I could hear her moaning and them both laughing and him grunting so I knew he was having sex with her. Naturally I got a real boner as I listened to them as she is very pretty and imagining having sex with her was turning me on. With John so close I didn't dare do anything to myself especially as I only had a thin sheet covering me. I lay on my side facing the wall, my hand clutching my hard dick through my boxers.
To my surprise I heard a noise from John's bed and I quietly turned my head and to my surprise, in the dim light I could see his sheet rising and falling. He was masturbating as he also listened to the sex noises coming from next door! I guess he thought that as he couldn't see the top part of me because of the open door, then I couldn't see him or he thought I was asleep. I kept very still as I didn't want to embarrass him but with sex going on both sides of me as it were my dick was throbbing. It was so frustrating not to be able to do what I longed to do, which was to bring myself off.
Then I heard my brother and his girl climax, as far as I could tell at the same time. Then I heard a quiet grunt from John and saw his body jerking so I knew he'd also come. I lay there as still as I could and when I heard a slight snore from John I knew he'd fallen asleep. All this time my hand had been round my rock hard dick so now I quietly rubbed it. Boy, was it on fire! The feeling in my balls was powerful and it didn't take me long before I was exploding. The sensation in my cock as my cream shot out into my boxers wrapped round it was one of the most intense I've ever experienced. Because I had to keep quiet and fairly still I think I almost passed out with the intensity of the pleasure.
So thanks brother and Jenny and also John for giving me one of the most memorable masturbation sessions of my life! Remembering it has inevitably got me hard again so I'll sign off. Hope you enjoyed this account of my experience.