For me, this was a pretty central concept (what Rich was talking about). My older cousin was always talking to me about what it meant to be a man, that he would teach me how to be a man, etc. etc. He was like a brother to me, and after my school got redistricted and almost all of my friends stayed at my old school, I viewed him as a very close friend. He began molesting me when I was about 6, and as I grew closer to him and admired him more, I just took what were doing as things that friends do together, even though I thought it was a little bit weird and seemed like something that I shouldn't be doing.
After I found out what had been happening was sexual, and therefore by definition a bunch of "gay" sex acts (in quotes because it was between two men, or boys rather, I guess), I felt horrible. I wanted to throw up. I thought my world was going to end. So I did what many distressed ten year olds do and I told my parents. They talked to my Aunt, and that was that. I told my cousin the next time I saw him that I had told my parents what was going on. He seemed just as freaked out that I told as I felt for realizing what happened.
That was the end of that relationship, but I realized for a while after that that I just assumed some amount of acting out was part of a friendship. I didn't have any friends anymore at that point, and I remember I asked the first real friend I made after that to act out with me. I was in fourth grade. He said no, and explained friends don't usually do those things with each other.
Years later, I count myself lucky that he's still my friend. We are now 26, and he's always been there to help me figure out what I'm thinking. Knows my obsessive nature, knows about the abuse, everything. The perfect friend for those times when I'm freaking the fuck out but can't talk to anybody else about why. More importantly though, I realized that friendship really didn't have anything to do with sexual anything, I just wanted some god damned friends and to stop being picked on and to stop being an outcast and to stop being bullied!