What to do when you find out your mother-in-law is cheating on you?

Hey! I'm similar to yours, I also found my mother-in-law cheating, just did not expect is in my father-in-law's eyes, my mother-in-law is a very smart person, people look young, and love to dress up, I really hate such a self-righteous woman, obviously their own is a bunch of piles, but also left and right to pick on other people's faults, and sometimes can not help but want to poke at her, but also afraid of brewing a tragedy