Your mom tells you she's having an affair. The man makes her happy and they work together. This man is married. She asks you not to say anything to ANYONE including your older sister. Your mom tells you some of the "cute things" he says to her. Looking through her phone one day to find another message, you come across one of their conversations. It has details including them hinting at the sex they've had at work before and other details I will spare you all.
What would you do? You're keeping this a secret from everyone except your S/O and best friend.
Would you tell your sister? Would you keep it to yourself? Would you tell your dad?
ETA: I'm the product of a previous affair with a different guy, I have no where to go if I get kicked out and have a 4 month old son.