I want to be friends but...?

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 mothns and I still can't stop thinking about him adn I get upset and cry I really miss him and it feels like someone close to me has died or soemthing. I don;t know how to let go