Im wondering if he likes me?

Ok, so there is this guy at school and whenever he sees me in the hallways, he always smiles. He recently broke up with his girlfriend. But I have noticed that he hasnt been smiling at me much anymore. Is it because sometimes when I p by him, I am walking with another guy, or he doesnt like me anymore, or maybe because I dont really smile back, or he just like me anymore because of that and just gave up?