How do I get this teenage boy off my mind?

There's this boy that I used to go out with and her lives right down my street. We broke up about two years ago. He sometimes comes to my house to invite me to play manhunt with him at night with some other of his friends. So I usually go and play with them. Just the other day he called my house and asks me if I want to go out with him and I explain to him how I go to another school and I have so much homework that I wouldn't be able to see him. He is a decent kid but I just don't want to go out with him any more. But the last few times that I have been hanging out with him I've kinda been attracted to him. So during the day I usually walk my dog down the street and he comes out and starts checking me out. I don't know what to do, I don't want to go out with him, I just want to be friends.