Need of help to get someone to show their real self

Hi! I am in need of my ex to finally tell the truth to his former. She has no idea and thinks I'm lying so I need him to spill his guts to her and be honest about everything. She messed with him while we were together. She manipulated the situation and I'm sure has her claws in his brain. But he hasn't let me go and lies to me about her. But texts her still even tho he isn't with her and has hung out with her! He needs the truth to come out and she needs her bs sent back to her. I know a good break up one and to shut her up just put her in a freezer but the truth one? Or to show the monster in each of them. I don't like her but I also don't know how else to get her to see the difference in who he was to me years ago to the ugly man he is now. She needs to not believe him and spare wasting years off her life over someone who's just gonna cheat and lie horribly to her to the point she loses her mind like I did. Please help 🙏