He’s choosing the route of blaming you. Ok, many people choose to go there, mostly out of self protection. We all know how painful it is to feel responsible for a relationship breaking up (something he’s been trying hard for you to feel huh?) so it’s not unnatural for people to go to great lengths to avoid that feeling. “It’s not my fault, they did xyz.” Or “if they hadn’t done x, I wouldn’t have done y. So it’s their fault.” That’s what he’s doing. Thing is, for most people, that justification method doesn’t hold up very long. There will always come a time when they have to look at themselves, whether it’s now or in 5 years.
In the meantime, hang on to your truth. Stay firm in what you know happened and is true, regardless of his opinion or viewpoint. With all the things he’s done, he’s sort of lost the right to have his viewpoint seen as equal and valid, I’d say. You’re the sane one in this scenario.