How can you tell if your best guy friend likes you but he already has a girlfriend?

You call him your best guy friend, but if you don't know whether he likes you or not, he's just a guy that you like a lot. If he already has a girlfriend, he likes her more than he likes you. That doesn't mean he doesn't like you. If you remain friends with him, and he doesn't remain such good friends with his girlfriend, he may decide that he wants you to be his girlfriend. Of course, by that time, you may already have another boyfriend who is better than he.