Happy Bank Holiday. Here's a (((hug)) from up North.
I've just gone back and quickly reread your previous posts. In truth, this isn't out of the blue behaviour. The previous tantrums and threats to leave until you danced the dance and made it all right for him. The nastiness. The entitlement to an affair because he deserved to be worshipped and you weren't fitting the bill in his eyes. It's traits of a narcissistic personality disorder. There is a research paper that I read somewhere that reckons to prove that at no point during the formative years was the narcissist made to take responsibility for their actions. Somebody will have tried their hardest to smooth over the tantrums and bad behaviour that all toddlers exhibit. Some never grow emotionally beyond that stage. When he has hit rough points in his adult life (actually it's just life) he's thrown his toys out of the pram.
Some call it MLC; I am afraid I call it being a 'kn**' There are posters on here whose spouses have shown such bizarre behaviour that is completely off the wall that some sort of crisis has created a severe mental illness. Your H (and mine) are just showing their true colours. It's all about them. Most of their sentences begin with 'I' and when you focus your attention on yourself, well they lose the plot. How dare you? This is all about him and his entitlement.
He's following a script, like many narcissists before him. Therefore you must understand that this is not anything that you have done or not done.
You must must do whatever is necessary to protect yourself and the kids.
I suspect that your marital dynamic was a bit like mine and you will struggle not to try and smooth over the conflicts. It's tough to break that habit. It occurred to me yesterday that perhaps I am the female equivalent of Mr Nice Guy as I would be nice in order to get what I want ie peace and a pleasant atmosphere. Husband was definitely MNG though it's just that he didn't need anything from me anymore so he stopped being nice. I'm not sure how we lasted 30 years!!
He will roll in and out of feeling sad for the M, sorry for himself, being nice and being nasty to get what he wants and needs. Stay strong. Don't retaliate and let it roll off you. You are a separate entity to him. His shi**y behaviour does not mean that you are sh***y as well. The more that you distance yourself emotionally, the more that you will see what you want your way forward to be.
It's his circus. He's already got one performing monkey. You are not his second. You're strong Kirsty, that comes across in your posts. Just go and see that solicitor now.