Ladies, this is my exact dilemma at the moment. I can see many ways in which NSDH is different. He is calmer. He does seem more rational. In the more heated discussions he's not losing his rag. He often apologises.
But.
But. But. But.
There are still things there. The incident at the weekend where he was rude to someone for phoning after 9pm on a Saturday night. Yes, ok, he doesn't want phonecalls at that time, but maybe if I was there I would. I don't want to be in a relationship where I jump and feel dread if the phone rings after a certain time, fearing what NSDH will say about it.
Yesterday at counselling I sat and cried and cried and cried. I was remembering how things were this time last year - I was full-term pregnant. And things were awful. As I sat and recounted all the many things that happened around that time (low-level violence with backhanding me on my pregnant belly, grabbing my wrist, hitting me in face with pillows, etc) and how I felt, and how intimidating he was to me when the baby was here, poking at me, shouting in my face while breastfeeding, pushing me about the hall and telling me to pack my stuff in the days running up to Christmas. I just cried. I'm not sure I can ever truly get past that stuff. And a lot of you on here have had things much worse than that. 
But the thing is, maybe it's ok that I don't get past it. If I'd just fallen out of love with him, I'd still be entitled to leave him and divorce him. I don't need a big excuse. Even if he turns into a completely new and shiny person, it's ok if I say 'I just don't want to any more. I don't love you/don't want to be with you.' And while I do still love him, I do still fancy him, I still care about him, but I don't think I love him like I did. Him snatching DS2 changed something inside me about how I feel for him. I can't make myself love him fully again. And neither can you. And if you don't love him, well, that's all the reason you need.
But as you say, the difficult thing is the kids. Can you explain that to them now, or at least the ones that you feel will understand (DD1, maybe?). That even if their Dad changes, you might not want him back, he's done too much for you to forgive? And explain that at the end of the day he'll always be their father, but if you don't want him to be your husband, that's entirely your decision.
Maggie - you are already so much stronger than your mother. She brushed it under the carpet and allowed herself to shut her eyes to it. You are not doing that. You are different to her, and you will keep your kids safe. You already are.