Is it love or lust I'm feeling?

I've never been in love before so don't know what it feels like. This september I started sixth form and met this guy who soon became my closest guy mate at school. We never meet up out of school but we know alot of personal things about each other. We share alot of the same interests. Whenever I'm with him we normally end up arguing. I can't stop thinking about him. Everything reminds me of him. I've become increasingly pent up with anger and I think it has something to do with my undefined feelings for him. PLEASE HELP!