OP,
This is really not difficult to understand.
He's killed your love and marriage.
You have been in survival mode.
He thought he could bully and abuse you endlessly, but like most bullys he backed down when he realised he had gone too far.
He's a shit father and a shit husband.
If he was otherwise he wouldn't have behaved the way he did.
His abuse has killed your marriage.
Denying that will do you no good.
Your self respect and esteem are strong.
You are quietly repulsed by him.
My advice, is get counselling for yourself first to really tease out what you want.
I think you know what you want.
Counselling as a couple could be good as mediation for a separation.
Pretending to him that you don't know and think he was a nasty prick for years is not going to do either of you any good.
Framing it honestly, ......in that his behaviour was so appalling that your feelings have changed.
That you can't and won't apologise for having self respect.
That you loved him but HIS treatment of you when you had 3 very young children was so dreadful that your feelings have changed.
Reach out to family and friends and tell the truth.
You sound like a truly amazing woman to have had the presence of mind to retrain with 3 young children and married to a nasty bollix.
Hats off to you.
You are way to good for him.
You deserve better.
He's blown it.
I don't feel one bit sorry for him.