Stop judging. Your not a holy prayer book. You have committed many sins just like everyone else in the world. I dont know why she would be your concern unless you live with her. Mind your business. Vengeance is the Lords. When karma hits her make sure she will be able to cry on your shoulder.
When i was younger i used to judge people, then with life experience i came to understand that people do things that we may not agree with but they have to live their own lives and we are all bbelieve me capable of doing things as the years go by that we would not have thought possible at one stage.
Try to put aside your feelings about this ladies affair and look at her as a person, im sure that you will see positives in her, and its important in a relationship to make the effort for your fella.
remember we live in a far from perfect world and as you get oldeer you may do things that you arent proud of
i didn't think well of most of the families, but their private business is private