My father is being horny on main

My father had a terrible childhood, and he has always talked about not being like his asshole father. Recently, however, I accidentally discovered messages between him and some woman that most definitely were sexual. My mom has always tried her best to take care of my family and does not deserve to be cheated on. I don't know what to do. I know the right thing to do is to tell my mom, but I'm so scared and disgusted. My father is religious, and infidelity is definitely against it, but he has also called me a liar and manipulative on multiple occasions, even though he is the one sending disgusting flirty texts to some woman all night. What should I do?