she broached the subject with me and I opened up to her about my concerns
Please don't do this going forward. She is NOT on your side. Anything you say to her will go directly to him. Also, the reason she wants you to take him back is because she doesn't want him landing up on her doorstep. She sees him as your problem and she doesn't him to become hers.
says all he wants is to feel like he has a proper family unit and to feel like number one, and me retreating from him is causing him to be the worst version of himself.
NO!!! He was already the 'worst version of himself' before you stepped back for your own safety and sanity. Don't buy into his pity me self serving words to his mum. And 'feel like number one' means he wants you to shut up and get back in your box. In a good relationship no one is 'number one'. In a good relationship you are equals and treat each other with respect and consideration. That's definitely not your relationship, is it?
I’ve also been worrying all day about committing to leave, because he could end up moving to an area I don’t like, getting with a woman I don’t know which I’m not comfortable having around my children etc
Actually to me it shows that you do NOT love him. Because you aren't saying "If he loves another I will die!", you are worrying that he may take up with a woman who is unsuitable. That's a sensible worry but no reason to stay! I daresay that if he met a nice woman who was kind to your children you'd probably be a bit relieved that he's taken his abusive focus OFF of you!
his mum also said he feels like my family dislike him as a result of me talking to them for advice about him during our relationship and she told me I shouldn’t have done that
In other words, she thinks it's better that you have NO support that is 100% yours from people whose 1st loyalty is to you. That the only people you can confide in his family, whose first loyalty is to him. Nice.
Don't doubt yourself. You are doing the right thing. And don't talk to his mum about the separation again. If she brings it up say "I really don't want to talk about it. It's between XX and me" and needs to stay that way.