Why can’t they accept I’m not forgiving him?

My husband cheated on me, for A WHOLE 2 YEARS, until I found out. I’m close to my SIL’s (his brothers wives) but they keep telling me that maybe we can work things out. The other day I told them when our child was FaceTiming him in the morning his, well I guess now girls friend idk, was with him in the bed because I could see and hear her talking, and they were like you have to put an end to this if you want your relationship to work out. But I don’t! And I told them many times!! For me he is free to do whatever, we are not together anymore, we are working on splitting financials and custody, we are “friendly”, because of our child, but I’m done with him. I know he wants me to forgive him, only to continue his shit, and all his family wants me to be “the bigger person and move on”. I don’t know wtf is wrong with them, I don’t know how they expect me to move past that. And I don’t know how to continue a relationship with them if they keep asking these kind of personal questions and I answer them honestly, but they still don’t have my back. How is any of that my fault? How am I the one that is wrong because I don’t forgive and move on? Should I just not tell them anything personal anymore and have a superficial relationship with them? I honestly want to cut ties with them, but I know it’d kill my child losing all the family after she already “lost” her dad 😔