This is such a difficult one to grasp…you obviously love him and just as obviously recognise the clear issues here.
You used an interesting word earlier to describe your relationship with him - ‘entwined’. I’d like to respectfully suggest ‘enmeshed’ instead.
I know what it’s like to love someone so controlling, how they convince you that boundaries are unnecessary, unhealthy, even. How they persuade you that constant contact is for your peace of mind, not theirs. How they start to redraw your priorities so you first let go of time with friends, then family in deference to time with them. Because you love each other and get to spend so little time together thanks to work or other commitments…surely you don’t want to give up what little time you have left together, do you?
When things go their way, they are the most wonderful of partners - warm, thoughtful, caring, funny and with a capacity for love that outweighs anything you could ever have thought to experience. If you texted them at 3am on a Tuesday to complain that your pillow’s too hard, they’d cross the country right then and there to bring you a softer one without a thought. But as soon as you do or say something they disagree with, they become cold, distant or angry…and so disappointed in you. You obviously didn’t care after all. They’d do it for you. They’d cross the country with a pillow in the middle of the night. Why won’t you just do this very reasonable thing for them?
When you’re with them 24/7, it’s suffocating, unsustainable but when you’re apart the thought of not being with them at all…the wonderful, caring version of them at least, it’s too heartbreaking.
If any of this resonates with you…OP, it’s probably not his fault, exactly, but it doesn’t make it right. I’m not saying leave him, I’m just saying to make a list of every interaxtion that happens between you and work out what you’re OK with and what you’re not.
If you’re not OK with an open mic then get him one of those button alarm thingy that calls you if something happens. There’s remote sensors that can text you if he has a fall or a seizure. They’re really good now. If you don’t want him to chain-smoke at you, then say you’ll only come round if he hauls himself outside to smoke. If you think his house is a mess, be clear that he needs to get help in to clear it if he wants you to stay over. If you don’t like how he talks about your colleagues or work, then be clear that you don’t appreciate it. If you want to go home at ten, then set out the schedule to him and stick to it. And if his negative reaction to that is not ok for you, then tell him that you won’t accept that behaviour from him.
For every interaction, ask yourself ‘is this ok?’, and if it isn’t ok, then say so. Set and maintain those boundaries because you might not live together but he’s still clearly controlling your every decision and your emotional state, even in areas he has no influence in, like your enjoyment of work.
Even separate, you’re still enmeshed.
A wise man once told me that the submissive partner draws the picture while the dominant one chooses how it gets coloured in. However, you are living in his picture, not your own and held there through guilt, duty, love, friendship, history and that awful knowledge that he’s dying, so how can you not?
But you can care about him as well as look after yourself. One does not negate the other and the latter is extremely important. Do you want to get to 62 and realise that you’ve not done a single thing for yourself in a decade? That you don’t even know what your picture would look like? Only you can answer that question.