What should I do! I mean he likes me I like him but this is how it goes!?

ok well theres this guy at my school that i like ALOT! since the first day i met him its been like... dang! but he has a girl and they've been together for almost a year now! but when they wasnt together he told me him likes me alot! and he so ku and sweet but thats only when its jus me nd him! when we with his friends or his girl he a total jerk! he made me cry a couple of time jus because i know hes two faced! what should I do?