This happened my freshman year in college.
First of all, this site rocks. I have had countless orgasms sitting in this very chair reading all the great stories.
Anyways, my first year of college I moved dorm rooms about half way thru the year 'cause I didn't get along with my assigned roommate. A guy down the hall had a room by himself and we got along pretty well so he asked me to move in. He had this girl that came over every now and then, and when she came over I would leave to give them their privacy to have sex. Each night when I got back he would tell me what happened and how it was, etc. This always got me very turned on. After we were done talking I would usually go down the hall to take a shower (this was late at night). I was so turned on by all the details he told me that I would go into one of the stalls in the bathroom (toilets) shut the door and jack off. If someone came in I would just sit there like I was going to the bathroom. This happened a lot 'cause I didn't want to do it in the room 'cause there wasn't enough privacy.
Well, one night we were talking about him and his 'sex-friend', and he suggested we watch a porno. I said I wish he would've told me he had a porn, but he said he only watched it when he knew I was at class or gone for the night, etc. Jokingly I said 'Boy I wonder why you only watch them alone!' We both kind of chuckled but left it at that. So we started watching the porn and WOW! did I get a raging hard on in less than a minute. I wanted to jack off so badly but he was right there underneath me on the bottom bunk. The lights were off so I jumped off my bunk (hoping I would catch him jacking off, but he wasn't...I could see a bulge in his shorts though) and said 'I'm tired, I'm gonna take a shower and go to bed.' He said, 'If you're gonna go masturbate why don't you just do it here, I don't care!' I was speechless for about 10 seconds (it seemed like 10 minutes) and then, thinking what the hell, said 'You don't mind?' 'Nope,' he said, 'I just assumed that's what you were doing all those nights in the bathroom anyways.' He told me he jacked off in the room all the time when I was gone, so we shouldn't hide it from one another anymore, and just do it when we wanted to. That was all the convincing I needed. I sat down on our small couch, pulled my boxers down to expose my already hard 6'cock and slowly started the show for him. He didn't hesitate to join in and soon we were about five feet from each other both with throbbing hard ons jacking off. It was such a turn on!! We were both just staring at each other's blurred hands going up and down on our shafts, I knew I'd blow my wad soon. So without asking I got up and stood over him at his bed and kept jackin'. He didn't say anything! I started to feel my balls tighten up and knew it was gonna blow! I told him,'I'm gonna cum!!!' He just arched his back, inviting me to cum all over his stomach. (or at least that's how I took it.) So out came the first white sticky rope of cum right across his abs. He actually sit up in bed to move his hard cock so I could cum on that. The next 4-5 cum shots landed all over his hand and cock, lubricating it for him. WOW! What a feeling! He came about 5 seconds after I did all over his chest and stomach and the rest just oozing out onto his cock. What a night! We both cleaned up and just kind-of were smiling at each other. That was the first of many mutual jack-off sessions between us for the next couple of months. Nothing else ever happened besides us jackin' off together, the rest of the year. I transferred schools at the end of the year and we lost touch. But that was probably the most fun 5 months of my life!