So long story short, my ex is a horrible person. He cheated on me, and I found he had been using dating apps for our whole relationship. I met up with him a few months back in a moment of loneliness and he stayed with me for a week. He lied to me about his dating situation and pretended he wanted to try and work things out. I have now discovered, he has a long term girlfriend who he is living with. I want to tell her he is cheating on her but he is threatening to share inappropriate photos of me if I do.

Would you tell the girlfriend or just move on with your life?