They didn't get drunk at a college party and mess up.
I don't really have a problem with that either.
I also realize that people change.
Not stuff where the bf knows and watches but where the girl goes to do a porn and the boyfriend doesn't know and she does it behind his back.
I could go on and on for the reasons this happens, but they should be obvious to anyone who went to college at a school that wasn't tiny.
I am not meaning to say that someone who cheated 10 years ago when they are 21 should still be a social outcast or that I would even think of them as a shitty person.