How do you deal with cheating mom?

You need to confront her. Ask her why and let her know you know. Sit and talk with her. Let her know how you feel about the situation ask her what she plans on doing with this situation.

This can be very uncomfortable especially if dad doesn't know. It's ok to let her know you know but she does not have to give you an explanation even tho you may want one. Trust her that she will make the right decisions for your family. If you don't feel you can talk to her you might consider telling your dad . OR you may want to talk to a friend. If you tell other family members it could cause fights. Myself I would try trusting her to do the right thing in good time.