Now you're overreacting again! Calm down a bit. First of all, I disagree with >>16. Hours on the phone talking with another man - instead of talking to you - is a bad sign, especially considering that your girlfriend said she didn't feel like including you in their threesome talks. If she spends more time with him than you, you are justified in being bothered.
I'm biased because I have a girlfriend too. Yeah, maybe it's selfish, immature and possessive to want her all to myself. But fuck, I'd rather be selfish, immature and possessive than risk losing her, especially to my best friend.