How do you know if your brothers friend 'likes' you?

First off, is he coming to hang out with YOU or your brother, his friend? If he talks to you more, or hangs out with you more than your brother, it's veryyy likely. However, if it's the opposite and he kinda ignores you, probably not.

Try to talk to him. His actions will tell you.. If he seems to give you mere answers and barely talks, probably not. If he seems willing to hold a convo you may have a chance.