You say turning your back on him wouldn't be right, but you CANNOT fix him, so what do you mean?

I know you said you planned on leaving him but are you going to divorce him? I hope so for YOUR sake -- get OUT of the house. Take the children, find a new life and hopefully find someone who wlll love YOU like you deserve to be loved and cared for -- and respected and cherished.
I hope you're not planning on "separating" but living in the same house like many people do. That's just plain insane. It's not healthy and it provides no room for a new life.
Anyway, you're probably right about past abuse. My late husband was abused as a child too, but he didn't act like that. He wasn't talkative until he met me, and then I was the first person he ever told about his abuse -- and he'd been married before!!! He just fell apart one day, and told me all about it -- and of course he was abused by a family member like most children are. He did get help for it, thank God and learned to deal/cope. I hope your husband will do the same.
Best of luck and God bless. Hugs, Lee