I really want to be his friend but he doesnt want me?

I really want to be friends with someone who doesnt want to be friends with me. I know I should just let go and move on but I have this weird attachment to him and I just can't let go. (it isn't sexual and I am pretty sure he knows that, it is almost like a brotherly or fatherly attachment [this he does not know and i would never tell him, that would be kinda creepy]) how can i forget about him? I havent talked with him in almost 8 months and I still can't stop thinking about him and I get upset and cry all the time. I really miss him so much and it feels like someone close to me has died or soemthing. I don;t know how to let go