Paranoid?

I feel really paranoid but I don't know whether it is really paranoia, jealousy or something more. Theres this guy I like and we talk a lot and have been involved for some time now, however whenever this other girl is around he goes and talks to her and it makes me feel like he just talks to me when she isn't there. Am I being paranoid or what?

I have asked him a million times and he says he doesn't fancy her plus she has a boy friend. Anyway he does talk to me when she's there and we go out on some weekends and have been doing 'stuff' but I just cant help but doubt everything even though he's said 'she's not right for me and we're just friends.