Immediate help needed

The man that I once loved and I just reconnected through social media. He told me that he had sex wit my brother girlfriend a few months ago. She had told him that she wasn't dating anyone that her man broke up wit her. He didn't know that she was wit my brother. I wanna tell my brother but he asked me to leave him out off it. My lover told me that she had sex wit his brother as well as the crew how should I tell my brother all of this without including my lover. I hate her so much cuz she knew bout me and him she know my past that I had with him.