Lots of PP suggesting that his new behaviour is just an act, and they may well be right.
However, let's just assume - for argument's sake - that this really is the new him and that he's turned over a new leaf forever.
Even if that is the case, you still have lots of trauma to heal from. And sometimes it's impossible to come back from that. He treated you very badly for a very long time. A single big argument where things are said in the heat of the moment is recoverable but where someone has chipped away at you over a long time, love just gradually dies. You can't force feelings where there are none - and deep down you know this. But by not acknowledging this and trying to force yourself to go against what you really know, your subconscious is trying to make you listen - hence why you feel so anxious and ill. (No judgement as I've done exactly the same as you in the past).
Still assuming he is genuine and no ulterior motives, he's going to be terrified that you'll leave him again. He's seeking reassurance constantly - especially as you're not connecting via sex. There are plenty of posts here from females who get clingy with their partners when they think they're about to be dumped. Same thing here. It's suffocating and despite what he promises, I think you'll constantly feel smothered.
Sometimes things are just too broken to fix, even if logically you want to. You can't make your heart feel what it doesn't.
You could try counselling. I'm not sure if would achieve much but it might help you both to process a split more amicably.
If you really do want to carry on trying, you could maybe try a date night and seriously consider having sex. Sometimes physically reconnecting can spark old emotions. Just to be clear, I'm not suggesting that you SHOULD do this - just that I've seen some posters on here try it, and sometimes it helps. Most times it just solidifies what they already know and makes them feel worse. Might make him clingier too. As I say, just trying to think of alternatives other than "it's clearly over, leave him" because I appreciate how difficult that might be for you with your DD.
If - and it's a big if - you want to continue, you have to view this as a new relationship, not a continuation of the previous. You need to rip up what happened in the past, and treat him like a new boyfriend you're just getting to know.
But honestly, setting all of that aside, I find it hard to believe that these changes are permanent. And it's not just about what he's doing, but what he thinks. Some of the comments he made before were derogatory and demeaning, can one person's attitude really change that much?
There's a post somewhere on here from a woman who had an affair, her husband found out and although angry wanted them to work things out. They'd had a terrible relationship so although not a smart move, the affair was her way of coping. Anyway, she tried and tried and tried to make things work - and her comments were very similar to yours, she just couldn't muster up the feelings and he was clingy. They eventually split and he's been horrible. It might be a useful thread for you to read through.