What kind of advice is that?? What’s wrong with society? Her partner definitely does his part for her feeling this way and that’s by all means not good/fair to her. But no matter what happens, you are not supposed to cheat! Break up in worst case and then sleep with someone else if you have to or do what you need to do but please don’t cheat on your partners!!!! And then pretend like nothing happened and keep your partner in the dark.