My step son spoke to his mother again

My step son almost relapsed... He wanted to go drink and shoot up again... Instead he ended up self harming... This is all because his mom decided to defend herself about signing her rights away from him and saying someone who sexually abused him. She made several posts telling HIS story and lying about so much. Even a few people in the comments commented how she contradicted herself. My step son called his mom yesterday and said I can stay. This time was different... He was calm.. She started with her nonsense and he was responding calm and mature. She actually called him a liar when he talked about her friend Jessi sexually abusing him and he said "Yes Megan(her name) because you were there". She got mad about him calling her by her first name and he pointed out how she was signing her rights away anyway. I'm not gonna break down the conversation like I did last time. Basically the same think. She was neglectful and let him get sexual abused and she calls him manipulative and gaslighting and attention seeking for holding her accountable. He told her to quit posting about what he went through and making him relive his trauma. One thing she said that annoyed me was her saying "Signing away from you is bes for me. Good for you too since I won't be sometimes there sometimes not". He said "I'm sorry. When were you ever there. My youngest memory was walking home from preschool because you didn't want to get me". Of course she plays the victim again and blames every dad thing that ever happen to him in him. I am proud for the last thing he said to her. He told her he went through hell and she never cared but he no longer needs her. That deep down she knows she's a shit person and doesn't want to face it so she runs from it and turns everything on him, but he told her how she sees herself is her problem and she can live with herself. Then said "I'm gonna go help my pregnant mother make dinner. Whenever you're ready to just sign me away tell dad. Goodbye Megan". And we made dinner together❤.He's becoming a man!

Edit: He's in therapy and outpatient rehab. His therapist is now seeing him twice a week since the self harming.