Just found out my mom cheated on my stepdad

Ts sounds like a Reddit story but I was on my way to the bathroom and I overheard my mom on the phone with her therapist. She cheated on my step dad 2 years ago for a year.

I heard her say she feels bad and guilty but she also said she could never tell anyone because she would be the villain so I don’t know if she actually feels bad or is just afraid of being painted as bad

Thing is she also cheated on my bio dad which I chalked up to him being terrible cuz he was abusive and she was looking for an escape but the new guy my stepdad isn’t bad he just gets jealous and is a bit temperamental. Not abusive. He means well tho

My mom and my stepdad have a child together, my sibling.

What do I do?