Hello My name is Dave, this girl that I like is going out withthis guy. He's not my friend and not my enemy, but between. And she doesn't notice me much. Should I just wait? I don't know.

You don't do anything. She has a boyfriend and is totally and completely unavailable to you.

You do nothing. She has a boyfriend, she does not want you. Move on.

Leave the girl alone, she's is not a trophy, she's in the relationship. Do not waste your time on something like that.