I’m so sorry you’re going through all this, it sounds like hell. I can’t give much advice, but didn’t want to read and run. I do want to say that whether your husband is a narcissist or not, his affairs were not your fault. You were and are good enough, he just wanted more because his bucket has a hole in the bottom, and is thus always empty.
You don’t have to do this, but a lot of people who split from narcissists find going minimal/no contact or at least ‘grey rock’ can help somewhat. I appreciate it’s not always possible, but they are good methods of self preservation when you can employ them.