Cheaters rarely cheat only once. If she isn’t honest enough to ‘fess up, she will likely cheat again. Take Bill Clinton as an example. Her husband deserves better. I would divorce her, but he may be a more forgiving man than I am. The truth is almost always the right thing. She should tell it and let the chips fall where they may. If her husband is truly “Amazing” as she claims, he deserves better than her.
I’m guessing that he already knows what she’s about. Rubbing his nose in it won’t help keep their marriage together, nor will it help their children.