OMG....I cant believe it. What should i do?

So this guy jst told me he has a crush on me n i feel the same. He ws really excited tat i said tat bt the problem is...he has a gf. I played bball wit his gf n she ws really nice to me....what should i do? Should I go after him or should I jst wait or should i move on? He always makes me laugh n he cares a lot. he makes me feel better wen i am upset. What should I do? He's the best thing tats happened to me so far.