@carloscarlos, I think you're right to expect that it will be hard.
But come back to us and take it one battle at a time.
It'll be the usual cycle of shock, self-pity, pleading fake niceness, anger, silence....
No doubt you'll go through this cycle a few times before he gives up.
MY mistake was to try and make my x understand why I'd had to leave.
I spent about two years trying to phrase it this way or that way to try and make him finally finally understand that I'd had to leave.
He was never going to give me his 'blessing' for having left him! Never.
so my advice to you now would be NOT to defend yourself. He may well use your former niceness against you. Ie, you probably identify with being a nice decent person and so you will be called a cold hearted ruthless bitch for leaving.
Dont' waste your time defending yourself or trying to get him to understand. Don't waste your energy or your time putting your 'side' across. He will deliberately never get it. He is not going to see the light, or if he does, it will be a ploy to bring you back to heel. Do not fall for it.
If he accuses you of being insane, impetuous, ruthless, cold-hearted, just say something bland like ''I did what was right for me'' and do not drive yourself prolonging it for years.
When a man is so crazy you have to plan your escape in secret they will never, ever acknowledge that they were an arsehole to you because that is going to challenge their entire world view.
Try and fast forward yourself to the point (that will come!) where you do not give a fucking rat's ass what he thinks of your departure. You won't get their for a while and he will no doubt be able to manipulate the fact that you feel guilt at cuasing him inconvenience which he will say is pain...
Do not put yourself up in the dock defending your decision to leave.
Stay safe.
I hope that you have somewhere safe to go and that the people around you will buffer you.