I like this guy and he likes me but he has a girlfriend. So what do I do about this?

Your only here once, so understand this, there are no rules to this game other than the ones you place in your own mind. Delete all the programming you received, the ones who get what they want in this life take it. No person in power, no person with money, and certainly no person with the person they want in this life, hesitated, or asked others if they should, or didn't flat out take what they wanted. Worse case the guy says no way, and that is still a good outcome because you won't waste any more of your life in limbo.