Thisis:
You are not his therapist. You cannot fix him. And most importantly, he is not you.
Because you are making progress yourself, you are over-hopeful about his. He is not the same person as you and it is most unlikely that his prognosis is anything like as good as yours. He may improve, well great, but he will never be "normal" and it is likely to be decades, not months, before he's even safe to be around. Don't go saying "but I'm not normal either". You've always been several hundred degrees more normal than he is. That's why he has to destroy you, remember? Nice, talented, decent, the perfect victim. It's one hell of a long stretch between "I realise my family were toxic" to "I admit I tried to ruin your career and your mind and your skin", even further to "I am truly sorry", and he may never get to "and it will never happen again" (in truth rather than in word; he's a good fellow with the words, isn't he?).
By all means feel sorry for the poor fucked-up person that he is, but at a distance. He will still hurt you if he can. You see small signs of hope that at least he's seeing his demons for what they are, if not exactly conquering them, but remember how much you thought he'd improved before and then remember what he did. You cannot afford to give him another chance. He will hurt you, perhaps kill you, and he may well do this in front of your DCs, who have seen more than enough fucked-upness already.
Don't let him in. Somebody else is helping him. Great. But you can't. Simply because you are his ex-lover and you still care about him, you can't. Don't even try. We don't want to see you in the papers in the wrong way.
And cry if you must, but cry for yourself and for the things your toxic family and partners have put your DCs through. You can mend it for them, the next generation, but only by keeping them far away from the evil influences that nearly destroyed you. This is one thing that you are best placed to do, because you've seen it, you know what to look out for, you can protect them. It is not too late for loving, sensible parenting to give them a decent future. Your H is in a different position altogether, one where it is too late for parenting and love just gives him an angle. Yes, pity him. But like a poor sad caged tiger in the zoo, don't go in and pet him, because you will lose an arm. Again.