........this is weird..........
i have done similar things while dating someone, stayed with a guy friend, hung out with a bunch of guys, et cetera.... never once was it a problem, if your girlfriend is at all smart she wouldn't waste her time dating someone if she had an interest in other guys. seriously, i don't think i've ever even intentionally or consciously flirted with a guy while i was in a relationship. i think you should break up with her anyway, you clearly don't trust her so...