Bill3 makes a good point that your gut feeling may be too strongly influenced by your FOO (family of origin) at this point. Do reflect carefully and don't rush into anything.

The scenario where your mother will direct the three of you to "talk it out" seems very heavy handed and controlling. As an adult, no one should be managing you to that degree. You have say about whether you want to do that or not. But that's also pretty typical in enmeshed families. Those are some of the hardest boundaries to learn to implement IMO. Our relationships with parents sometimes don't transition well from kids who need guidance, to adults who are autonomous and get to make their own decisions.

I don't want to get into my situation too much- for the sake of your needs from this thread- it's complicated and unusual. H has developed physical, mental, and rare neurological issues in middle age that seem to have changed his personality. No one seems to know where one medical issue begins or ends, so it's just messy. The enmeshment may be one of his lesser issues at this point.

Looking back, there was always an enmeshment, a vague feeling that his family came first, but when he began to struggle with his health issues, it was like he emotionally abandoned DD and myself, and went all-in with his FOO once again. His FOO seems to have capitalized on this.

I don't think he has it in him (possibly not even the capacity/ability at this point) to separate from his family. It might be too scary and painful for him. If he was capable of implementing boundaries with them, it could essentially mean being cast out of the family. They very much have a "you're either with us, or you're against us" mentality, which doesn't allow for much independent thought or action. It's an echo chamber, go along to get along. If you don't, then you're considered an outsider. He had less of a problem with this in the past, but the anxiety or whatever from his current problems make him insecure and needy enough to cling to them at all costs.

I hope you find your way, and learn about some new ways of living that are freeing and empowering. Your H sounds like a really good guy, but I can also understand the powerful nature of an enmeshed family. Lots of hugs and prayers for you.