My mom is cheating on her boyfriend with a married man. What do i do?!?

First of all don't judge and talk crap about my mom. I was switching phones with her but before i did anything i wanted to send all my pictures and videos to her phone (which was going to be mine)anyway so while i was sending my stuff to my new phone i accidently read a message that was all like "i love you baby.so are we still gonna continue our relationship?"and i pretended to be her and i txted him back.(i know it was wrong but i just had to know if something was going on between them)and something is.i found out they met up yesturday and she was practiclly gone all day.she's a hyprocite.because she tells me not 2 cheat on my bf (and i don't) yet she's doing it.i really like her bf now and i really want to confront her i just don't know how...and i was going to do it tonight but her bf is spending the night and i didnt' want 2 start anything.also i want the other guy's wife to know.this is really wrong and i'm so dissapointed in her. please help? :(