How can I get over a guy friend?

So I've liked my friend for a couple of months but he doesn't like me in that way. I told him I liked him about a month ago and he told me he just wanted to be friends, which at the time I was fine with. But recently I've been getting slightly depressed at the thought of just being friends (and yes, I know how stupid that sounds). We spend every lunchtime together since we're in the same friendship circle and everytime the conversation turns to (being 17 this happens kind of often) I feel like smashing something! Please help me get over him!?