OK.... It's tough for me to do this, but here goes.....
I know the kind of dodge ball incident you write about. I think they have been a pretty common thing through most schools. Everyone knows what dodge ball is, although that doesn't mean everyone liked it. You had to at least "pretend" that you liked it, even if you didn't, and even if you were getting the shit kicked out of you one way or another. Otherwise you would have been an outcast, something no one wanted to be.
I was the guy on the other side of the ball. I would have been the one throwing the ball at the kid who got isolated. I wouldn't have started it, but I certainly would have joined in. Athletics were my thing. I have to admit, however, that after I was raped at age 11, I didn't pick on the loner, because I felt I now was one. I was always good at athletics, but I became a lot more aloof and unwilling to beat up on anybody who was being made fun of. After that, all I wanted to do was play, although I became the dumb jock. I am sorry now for the way I was, and sorry that I had to grow up that way. I was pretty stupid.
I can see why you have trouble separating the physical violence from the sexual harassment. Remember that sexual assault/rape is not primarily an act of sex. It is an act of VIOLENCE. It took me a long time to get that. So you've lumped all the violence together, even though there are different facets to each one. And it also hurts when friends are perpetrators. Your friend was a bully, and you were used by him to get acceptance. He clearly didn't accept you for who you are, and that's what true friends do. And because you've had bad experiences with one individual doesn't mean that everyone is like that. Most people are good, and we have to remain open to friendships. If we don't, we miss out on a big, often rewarding element of life.
Hope this helps.