Caught my dad cheating on my mom, what should I do?

While laying in my bed trying to sleep I heard my dad get a call. It was 11:30pm but I didn't think much of it until I heard a woman's voice. I realized they were video chatting and that instantly made me suspicious.

(Bit of a backstory here, when I was 12 years old I caught my dad cheating. I saw him texting a woman, calling her baby and saying some explicit things and I told my mom. They argued a bit, but then it never came back up. My mom's not the type to forgive cheating so he probably convinced her that I didn't know what I was talking about.)

So when I heard this woman on the phone with him, my mind instantly went back to that moment. I confirmed it was definitely an affair and with the same woman. They told each other "I love you" and that made me even more sick. I'm 17 years old, so I know for sure this has been going on for at LEAST 5-6 years. I'll be 18 soon and my brother just turned 15, in 3 years my parents won't have any kids in the house and that makes this even more difficult.

Do I tell my mom again, do I confront my dad first, or do I stay out of it completely? This has been weighing heavily on me since I was 12 and it completely ruined my relationship with my father. I don't think I can hold all of this in again...
Tell my mom
Talk to my dad
Don't say anything at all
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Caught my dad cheating on my mom, what should I do?
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