Someone I considered a “friend” went behind my back and is now fucking/dating my ex (which is funny cause she said she hated him, he was ugly, and she would never ever get involved with him). True colors, right? How do you come back from that?
She’s a liar who felt the need to do your sloppy seconds, so the bitch obviously has issues. Don’t make them yours. She’s the one who’s pathetic, not you. In fact, this isn’t even about you, not really, so do your best not to take it personally.
Just forgive her and move on. Cut her out of your life if need be, but in the end, she deserves your pity rather than your contempt, and she certainly doesn’t deserve the power to upset you, so don’t give it to her.