What to do about SO who I feel did wrong

A little backstory

I am studying in england for the semester and my significant other decided to go to the club with some of her friends (she is in the states). Me and her have a thing where "if it would upset you if I did it then you shouldn't do it" which i think is a good idea.

While at the club she grinded and danced with 4-5 guys and the next morning told me but tried to play it off as it was nothing, or a joke. I did not find it funny because she specifically told me that if i were to go dance with a bunch of girls that she would be horribly upset.

the reason this ... effects me so much is that in the past she has cheated on one of her exes. So to me her trying to be flippant about this suggests that she could do something else. the real thing that bugs me is the hypocrisy of the event. She wants me to forget and forgive even though she would not if i were in her shoes.

So. what do? I figure i can either break up with her or punish her somehow, either by getting a "get out of jail free" card or some kind of favor. This isn't a relationship breaking thing, but I really want to hit home and draw a hard line so that she never even thinks of doing something like that again.