My friend has been going out with his girlfriend for almost a year now. Supposedly, he lives at home, but it's safe to say he lives with his girlfriend because he stays there every single night. Well, he was planning on spending New Year's with her and a whole bunch of friends, but now his girlfriend tells him that her friend (another guy who she thought she was in love with in the past, but never went out with) wants to come visit her for the holiday. My friend tells her that he doesn't really mind if he comes down, but he feels that his holiday may be ruined because of how bad this guy treated him when they met a while ago and how his girlfriend doesn't pay any attention to him when this guy is around (this is true, I was there). He also goes on to tell her that since he stays at her house every night (even when her other friends stay over, at her request), he doesn't see why he shouldn't be able to stay over if this guy comes to visit. His questions to me: -Should he worry? -Why would it be a problem for him to stay at her house when he's around, but it's not a problem any other night regardless of who else is there? -Is he wrong for not liking the fact that his girlfriend has another guy staying at her house alone with her? I really didn't know what to say because I'm good friends with both him and his girlfriend. What do you think?