7 year old is controlling my relationship.

I have been with my partner for a little over a year. He has a 7 year old son, who the relationship with the mother is very very toxic. She uses the child against my bf and makes him hate me and not want me around, tried to get me fired 2 times from my job at the sons elementary school. She tells the child I’m pregnant and we are replacing him, gets him to call me ugly etc. I’ve tried to give her a peace offering at Christmas. She freaked out, then said she over reacted, then freaked out again. My bf is overly nice and honestly is kinda a push over. She sends horrible messages constantly and he ignores them. My issue is that he lets his son decide what goes on. His mind is against me so he hates me randomly but loves me randomly. Once he goes back to his mom he hates me and once he spends time with me he gets used to me.

My issue is I’m ready to move in together and I think he needs to put his food down and let his son know I’m permanent, he doesn’t get to choose when I come over or not. He doesn’t get to make me sit in the back seat. He doesn’t get to talk rudely to me or throw shit at me. I honestly am the nicest person and have gone through a lot and try really hard and my bf says he understands the situation because I said you wouldn’t be okay with it if it was reversed. He said he wouldn’t but he knows because he is in it. So it’s frustrating because would he raise my kids like that?

Not sure how to talk to him about it because he says I knew what I was getting into from the start. It seems like it’s the kids way or it’s over and honestly I don’t want to leave him. I do love him, I do want a future but it’s just hard :(