Sister Ex
Your ex's ex with whom you have become friends. The friendship starts out as a trauma bond, swapping stories and comparing notes on the dude's lies, cheating, and manipulative behavior, and evolves into a genuine sisterhood.
I'm getting together with my Sister Ex on his birthday to wish him a year of pain and misery.
My sister ex confirmed he was cheating on her with me when we met.
My sister ex confirmed he was cheating on her with me when we met.