This is long...Please stay with me! My parents divorced when my bro and I were 5 and 6. My parents handled it totally wrong and for the sake of the kids, I am sharing this advice.
I know there is hurt and confusion right now, but you posted he will do anything for his kids. If that's true, please don't badmouth him to your kids (and make it clear to him that he is not to badmouth you to them). I guess you can even put this in your divorce decree. The kids are little and confused right now.
My mom badmouthed my father (and called his girlfriend the devil) for years to us. It was not explained why he left and there is anger and resentment to this day over it (20 years later).
If possible, you and your hubby should sit down together and tell the kids things aren't working out and mommies and daddies don't always live together. Stress to them that you both love them very much and it is nothing they did. They don't need a lot of explanation - they just need to know they are loved and are safe. It's inevitable they will see you cry - but try not to let them think it's b/c they're daddy is a jerk. I know it is why and he is a jerk, but in their eyes, he's their daddy.
You and dad are still the parents and are bound to each other at least until this newborn is 18, so you need to communicate with each other in a way to make the kids interests first and foremost.
I know this sounds like I am pro dad and what he did to you isn't bad. I'm just thinking of the kids (based on my childhood). He is definitely a jerk (I don't know how strong of language I can use here...), and needs to be held responsible for supporting his kids and responsibilities.
Based on your last post, he's expecting you to work with 3 kids and MS. Has he ever tried to take care of the kids full time? You do work - very hard and shame on him for his actions.
Keep your head up and stay strong. Love your babies and you'll get through this! I'll pray for you. Good luck!