Although I am straight, I had some of the most intense and fun experiences ever with my college roommate. I always thought he was attractive, and we spent a lot of time talking about women's butts, and doggy style sex. I could also always tell that he was aroused when we had these talks. I knew him for over three years and nothing ever happened between us until one summer night.
We had the apartment that we shared with several others to ourselves for a week, and came in one night particularly horny after seeing a lot of attractive women out. Somehow we wound up lying next to each other on my bed talking about this, and rubbing our own cocks. Our legs were touching, and I felt a tingle going through my whole body. His ass was back against my hip, and I finally got the nerve to go for it---I turned my hips towards his, and began grinding my dick between his asscheeks (he was wearing shorts). He started pushing his cheeks back against my hard cock, and moaning---I couldn't believe it was actually happening.
We ended up taking our shorts off, and he put baby oil all over my dick and his asscrack (something that had long been a part of our fantasies about women). He laid face down on the bed, and told me to get on top of him. There was never any kissing or penetration or anything, but I just rode my cock between his slick asscheeks while he gently bucked his asscheeks up and down against me. It was one of the most intense experiences I have ever had in my life. Needless to say, I didn't last very long---I felt the pressure building and cupped my hands under his shoulders as a continued to grind myself against him. Finally, I blasted cum all over his back and ass. After that, I did the same for him, much to his delight.
For a few weeks after this happened, we didn't speak a word of it (it was kind of awkward), but we did end up doing the same thing two or three more times in the next year when we had a chance. In the ten years since it has never happened again, but we can now talk about our shared and secret experience pretty openly, and we agree that for both of us it was one of our best ever!