How to talk to crush when he already knows I like him?!

So I'm in my freshman year of high school and there is a guy I like. He has a girlfriend but she goes to a different school. I told a few people about him and someone told. :P So now he knows. I'm not trying to steal him from his GF or anything but I would still like to be friends instead of having to deal with all this awkwardness. I don't know though if it's a good idea, how to approch him, or what to talk about. I already heard from a friend who talks to him that he thinks I'm obsessed with him. >__< So I don't know how to go up to him without it being so obvious that I'm trying to find an exuse to get close to him. What should I do?