I cheated on my gf with the guy that she cheated on me with
Why did you both cheat with the same person?
My mom said they were friendly, and we had never dated.
You shouldn't cheat on your partner just because they cheated on you. If monogamy doesn't work in your relationship, you should discuss that openly and honestly.
It doesn't matter, she is a slut and everyone knows it now.
You can't judge your girlfriend's behavior if you did the same thing. It doesn't make sense to insult her or hold her to a standard that you aren't holding yourself to. Cheating is wrong.