What should I do about him?

Agree with VOE.

Does she know that you are interested in the guy? If she does know, does she flirt with him anyway? If she does, she isn't your friend. If she isn't encouraging him and he continues to go for her, then it isn't her fault. If she doesn't know which guys you are interested in, then tell her. Since most boyfriend/girlfriend relationships usually are short term, do you want to give up a friendship for a boyfriend? You stop this from happening by a) being more self confident. Nothing is more attractive than a woman who believes in herself. AND b)don't take guys around your friend, at least not at first. Although she may not be giving any signals, the guys may think she is. VOE