In your position, I'd feel the same. It's simply much too little, much too late.
You're going ahead with the divorce, which will undoubtedly 'set him off' again, and I'm sure you know exactly how nasty he can be.
So you're going to need to 'grey rock' all his attempts to annoy you or to try to get you to reconsider divorcing him.
Initially, he'll keep up with the 'Look at me, I've changed' routine he's currently doing, but once he sees that it's not working, he'll change tactics.
Next he'll likely be very angry, and he'll do his best to involve the kids too. E.g 'Your Mums splitting the family up' and 'This is all your Mums doing, I want us to stay together and be a family' etc etc, so prepare a couple of 'grey rock' responses to that kind of tactic from him.
Then, once he sees that being angry isn't working either, he may try to make you jealous by dating other women, deliberately buying new clothes and going out a lot more, or he may try guilt by weeping everywhere and wearing a 'dressing gown of doom', because 'what's the point? My life is over, I might as well kill myself!'.
Whatever he tries, you need to keep calm and continue to gre rock him.
You also need to think about what you're going to do about your 'wife duties'? i.e Laundry, cooking, shopping etc and whether or not you want to stop doing those things for him? You will obviously keep doing them for your kids, but you no longer need to wash his clothes/cook his food/ buy food he likes/toiletries/ manage his appointments/car insurance/ family birthday cards/gifts etc, whatever you do for him now, he can do himself. He's going to have to learn how to do those things for when he's living alone and when he has the kids, so he may as well begin now?
It will take time, patience and determination, but you will look back at this time as the beginning of the lovely calm, serene life you will have once you're living separately and divorced.