I've been fantasizing about my friend
Oh really? What kind of fantasy?
I wanted to touch his ass since high school
Have you thought about reaching out to him and telling him about your feelings? It's okay to fantasize but imagine you can do it in real life? It would be like a dream come true, or else you might have regrets for not trying.
I masturbated thinking about him.
Well maybe keep that to your self until you tell him how you feel. It might come off pretty creepy. But I think it is perfectly normal to fantasize about someone you like.