So sorry you’re going through this. He sounds like my ex. I stayed for a long time, and then after I left I still stayed around and tried to help because I was worried about him. Tried and tried and tried and tried.
Sometimes I would read advice to other people like “oh he’s just abusive, abuse is not the same as mental illness” and I’d think oh but no! Mine really is mentally ill, he really does have problems, I love him, he needs me, I would be so so cruel and heartless if I just left him to suffer, even if it’s breaking me he can’t help it because he’s ill.
He was ill. He was also abusive. And he wasn’t really interested in trying to help himself. It seems odd to say “he liked his life the way it was” because he certainly wasn’t happy, but he was very comfortable with the setup where he either flopped around helplessly and I had to help, or he raged and hurt me and wrecked stuff and I had to help, or he did other things to ruin our lives because he “couldn’t face” anything he was responsible for, and again, I had to help. And because I could not fix it all for him - nobody ever could - he could then also rage/cry/sulk at me for not helping him.
I only left when he had made my life so miserable I couldn’t see any way I could stay and mentally survive. (We didn’t have DC.) He was awful in the short term after I left - which is why I stayed around, I thought he’d kill himself, I hated seeing him in pain and blamed myself - but it didn’t help him and it certainly didn’t help me.
In the end I moved away and cut him off completely as much as I could. I felt terrible, but the situation was destroying me. And then from what I can tell he sulked for a while, ruined a few friendships, ended up homeless for a time, phoned me blaming me for it al - and then I STILL didn’t go running back to him - and then he actually went and got help from doctors. I’m not in touch with him now but from what I heard last from others, he’s in a much much better place, settled, happy, under long-term treatment for mental illness. I am very sure that if I’d stayed, he would not be doing well and neither would I.
I can’t tell you what to do but I know how hard it is to cope when you think “sure he’s destroying me but he’s ill I must help him!” I was trapped there for a long time and it was awful, and I’d you’d told me at the time “you can’t help him, you aren’t helping him, just leave” I would have ignored you. But I wish I had left sooner.