girlfriend hangin out with best mate

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4 months ago my best mate broke up with his girlfriend of 2 years. He constantly spoke to my girlfriend and her friend about it. I work away sometimes and last time i went away he kept seeing my girlfriend even when i wasnt there. I told him i was uneasy with hoim going over to my house when i wasnt there and he was cool with that. But he still goes out with my girlfriend of 3.5years and her friends without me being there. At the moment my girlfriend, her friends and my mate are at the movies, i cant go cos i have to work early every morning. They have started calling themself a club as they go to the movies every thurs night for the last 6 weeks or so. Initially i saw it as an anti-me night and still do. I ofcourse dont have a problem with it except for that my mate is there with them. A few nights ago my girlfriend was pissed off with remarks made to her by my mae and her friends, i heard my mate tell her that he was up all night worrying that he had pissed her off. That sort of thing is not something that occurs between yaself and ya friends parter. I know nothing physical is goin on, ive been with her for over 3 years, but im suspecting an emotional affair, emotional infedality.

 

A few years ago a mate that was in our circle of friends broke up with his girlfriend, we no longer see him and he lost his friends yet my mates continued to see her well after they broke up. I know my mate has it in him cos he's done it before. Im considering putting this to the test to see if i would lose friends if me and my girl friend were to break up but not too sure how to go about it. There needs to be clear boundaries between who my mates are and my girlfriend's mates are. Im about to snap and hurt this guy, but then what? is my girlfriend emotionally involved with my mate and continues to see him? is my mate emotiona;lly involved with my girlfriend and continues to see her? Either way im pretty determined to make this the last time they go and hang out together. I never hung out with his girlfriend or any of my other mates girlfriends. Not too sure the best may to go about this... Ideas?