<human>: Can you provide a brief overview of the text?

I'll try to be quick, and sorry for my english, it's not my main language.

I'm 23 years old, and I've always had memories from many different times of my life when I was used by my parents as a kind of a peacemaker for their marry.
I'm not going into details about their specific acts, it is enough to say that my parents cheated and still cheat on each other, and the first occasion that I can remember was when I was 8 years old or something.

Yesterday was my dad's 53 years old birthday, and there was a party in their house, where my younger brother lives with them. Today I live in a city 2.5 hours away from theirs.
So, what happened yesterday is the peak of this whole history.
My brother called me crying at 4am, saying that he saw a friend (also married) of my parents talking with my mother in a very strange way, like trying approach her in order to have a kiss. And my brother says that he is 95% sure that he SAW that kiss. He somehow managed to remain silent for the rest of the party (I never would've managed to handle the situation the same way - he done the right thing), and then he called me after the party, saying that he couldn't sleep, and then he told me the whole story.

Telling my dad isn't a reasonable decision right now, since for him that would be like taking a shot in the chest, and he would want to kill his "friend".
I've spoken to my mother, very quickly over the phone. And she's coming to my city today to talk.

I think that's enough for you to help me somehow, I'm very confused about what to do, also because it's not the first time that something like this happens and affects both me and my brother directly.
Do you guys have any advices? I'll be very thankfull since this is a very bad situation to be in as a son.

Thank you!
<bot>: My mother cheated on my dad in his 53 years old birthday party over their house. My younger brother saw it. What should I do?