Leave for my mental health?

[Beetlewings]

Sorry in advance, I haven't been here for a while (this sounds like confession!) I am at my wits end and I wonder if anyone can advise me or validate me or whatever. I have been living with ex partner as I cannot afford to move out and it's been bearable but recently, after years of low level micro-aggressive, narcissistic behaviour I learned he had hit on my own sister, and tried to cover up by telling me she was "mental" (sorry, his words) it caused a two year division between my sister and I that we have been working on recently, it's been heartbreaking. All this came out during a very intense meeting between her and I and she is naturally as appalled as I am.
I'm not a confrontation type person, I wish I was but I literally melt into a puddle of anxiety when I try. So I find myself plotting minor, childish revenges, bickering to my friends, refusing to talk to him about anything that's not to do with children and when I do I am bitchy.. etc etc but it's not me and it is having an effect on my mental health.
I KNOW I need to leave with the kids (they are pre teens and obviously adore their father) he is super charming to everyone so I have few people to talk to... I am torn between thinking leaving would be just another act of petty revenge and thinking I need to do it for my own good. I stay for the kids. I don't even know why I am writing this - will I be able to afford to live? I have a couple months worth of rent saved up. This has come at the worst time! Do I stick it out? My job is part time and not that well paid. I'm not married and the house is his. I just want a calm life

Scan you not sit down, calmly say this clearly isn't working for any of us it would be best if we live in separate buildings, but first and foremost are our children. I need some help to afford a place, nothing fancy, where they are safe and happy, so can we try and sort something out between us like devoted adult parents.

And if he gets difficult I want 50/50 and not pay you etc. You get legal help. 50/50 means half of everything, all costs, winter coats, school trips, half pick up and drop offs at school, half holidays. Half sick days, half medical dental appointments. Get this all in writing legally. Then at least you might be able to take on more work.

Thankyou. Maybe legal help is the way to go. He's not the sort of person one can have a good conversation with, he's defensive and pretty much narcissistic. I've been treading on eggshells for years, it's all coming to light now I have had enough. But yes I wish I could do that, I think if I can't 'grow a pair' and have this difficult conversation, it can't be that bad IYSWIM ? I would need to ask him for money and that would enrage him. Currently he pays the mortgage and utilities and I pay for everything else.