Have you written your letter@Neverimagined ?
If so do it for you and keep it for future reference to read whenever you doubt yourself but I agree with all of the PPs who said DON’T send it otherwise you reveal your hand in any future negotiations because he will then work on defending all and any accusations in that letter and refuting anything you have said.
He knows what he has done. He is now trying to avoid revealing the monster he is to the world.
You might want to try this book:
POWER: Surviving and Thriving After Narcissistic Abuse: A Collection of Essays on Malignant Narcissism and Recovery from Emotional Abuse by Shahida Arabi.
Maybe listen to it on audiobook when the kids are in bed…
as he sounds like he has a lot of narcissistic traits and behaviours ie lack of empathy, a need to feel superior over you, a sense of entitlement, manipulation, gaslighting, mood swings, blameshifting etc.
It helps to learn the tactics of narcissists to see how to protect yourself.
He will try to ‘hoover’ you back in because if he can then he will think he can convince the world ‘look! It wasn’t that bad - she came back to me!’ So don’t ever go back… You and your kids deserve far better.
Youtube has some good videos on recognising and managing these narcissistic tactics (search narcissistic abuse) and as a PP said your best defence at the moment is silence as then he has nothing to get at you with and he can’t further label you as ‘crazy’ if he is not able to provoke any retaliation from you.
Sending big hugs. It is so hard but each day you are getting stronger, even if you don’t feel it. Xx