What should I do to get a guy out of my mind?

I've liked him for over two years. I'm really really shy around him and really I've never actually talked more than a few sentences with him. I talk to him mostly by IMs and he knows that I like him, he's cool with that. He's pretty sweet through the IMs and from what I see he's really really nice. Trouble is he's one of the more "popular" guys at school and I feel that if I did something say leave a note in his locker his friends would know and tease me about it in the hallways. I am kinda young for this (I'm only 13) and I know this should be a time when I'm focusing on education but I'm so obsessed with him. I've tried to get him out of my mind because he's graduating in three months and I'll probably never see him again. What should I do? I want to at least be friends with him before he leaves if not more.