Hi OP,
First, I have read the thread and don’t think anyone is intending to be patronising. Yes, people do speed ahead a bit...it is hard to read your words and not want to ‘get you out’ of it ASAP. Once you are out of an abusive relationship, you can still feel raw, scared, grief-stricken etc but we can all see your life would be better for the three of you without this rage-machine in your home. Of course you love him, I suppose I feel that if you love someone it makes you all the more vulnerable to the damage he can inflict. So that worries me.
This sounds very similar to my experience of marriage breakdown. It was incredibly one-sided i.e. he wouldn’t talk, would only shout. He either couldn’t or wouldn’t discuss how serious our situation was, and would not recognise how deeply unhappy I was. He also chipped away at my confidence, called me an unfit mother and was inexplicably cruel towards me.
I desperately wanted answers. I really thought I could find some sort of key to his behaviour. Because I couldn’t explain it. I agonised, probably for a lot of months, if not years. And it felt so tragic, because it seemed he was throwing away the potential for such a lot of happiness, home and family.
He never gave me answer and I never got to the ‘key’. I stopped trying to explain it, apart from acknowledging that to bring himself to be controllling and emotionally abusive, he must be a very damaged individual. And to think that I might be able to heal that damage in any way, was fruitless, thankless and impossible.
You want to do things by the book and so that when you look back at this, you will feel that you did everything to split amicably and with dignity and the best way for your children. Oh and you are concerned about his visa status as well. By any standard that is a lot to take on...for one thing, he is responsible for the visa consequences of his actions.
The sad thing is that he has effectively declared himself your enemy. You perhaps have not recognised this yet. And yes, you now need to go undercover - you know he is your enemy but don’t let him know you know that.
As to finding out the Why...have you heard of the book ‘Why Does He Do That?’ by Lundy Bancroft. It is extremely good...and although it addresses the ‘Why’, the main thing I learnt from reading it is that eventuallly you stop looking for why, and just accept that your DH’s behaviour tells you everything you need to know. ‘What’ he does is more important than why. But again, that might be speeding ahead from your current position.
Good luck, you sound like a good mother and you have a lot of strength...use it now before any more gets chipped away.