Emotionally abusive ex wants to have sex to erase "bad memories"

I'm recovering from a toxic relationship that ended last year. I tried my best to make it work, but unfortunately I was the only one trying. I was emotionally vulnerable and one night after a round of drinks ended up having a threesome with my ex and his friend. At the time it seemed okay, I even asked my ex if he was totally cool with what was happening and he didnt object. It was decided that none of us would speak of it ever again.

A few days later however, my ex started harassing me on texts accusing me of having an affair with his friend for a long time before the (Who was involved in the threesome) and blamed me for putting him through the trauma of making him watch his friend have sex with me! He blamed me for having orchestrated the threesome in order to get back at my ex for breaking up with me after promising to get married. He harassed me for over a week and that included threats to involve my family and his, suicide threats and host of abuses night after night. He said if it werent for the threesome, he would get back with me and marry me and that I am to blame for everything.

Truth is, he had broken up with me and had no plans of getting back or getting married, despite having reached the stage of getting married. The threesome was mutual and nobody was forced. He was hurt maybe looking at his friend with me which is understandable but at no point did he stop me or ask to stop it.

Its been more than 3 months since that incident, and he is still angry and hurt and blames me for everything. He is playing victim. I apologised for the sake of the relationship and to keep peace, but he said he would only get over it if i slept with him and helped restore his ego and erase the "terrible memory" of the threesome. He also shared the incident with two of his friends after promising not to tellnybody!

Meanwhile, I found out that he has signed up on a matrimonial website and is actively looking for a girl to get married to (LOL)
So when i confronted him about it he got angry and started abusing and blaming me again- and sent me pictures of potential matches and also said he had found plenty of girls who were much better than me. This really crushed me. I don't think I'm ready to see He knows I'm still recovering and hurting and unable to move on, but continues to blame me. He's playing mind games with me and is seeking revenge. I think his plan is to keep having sex with me and find somebody else in the meanwhile in order to get revenge.

Cutting him off is something I've done multiple times but havn't been able to sustain it for long. I end up contacting him. I know i deserve better, but im moving in circles. I cant get out of this mess.