What to do about my girlfriends guy friend?

I have been going with my girlfriend for 5 months and it has been going so good that we have had discussions about moving in together. She thinks we should and even though I see a real future for us, I want give it a little more time for the relationship to develop. The problem is she has this guy friend, I have yet to meet, that seems to keep popping into the picture and causing problems. The first time was when I found he wanted her to drive him to get a vasectomy when he already has a girlfriend that I think should do this. Now I found out she has been talking to him about us moving in together and he is telling her that if I really loved her that we should, which is causing her to be upset with me. I also find out he told her that he wants to leave his girlfriend because she is not the right one. What do I do about this guy? Should I tell her that I don't like that she is seeing this guy, as it sure seems to me that he is trying to sabotage this relationship?