I have a relative in the same position. Her husband has a lung condition due to years of heavy smoking. He has never seriously tried to give up, even after having throat cancer he couldn't or wouldn't stop. Over the last decade his health has declined rapidly because he doesn't act on any of the advice that the various healthcare professionals that work with him advise, so that now he can do nothing. He's not old, but he looks and acts like a frail 90 year old.
Sits in the chair in his pyjamas and dressing gown, doesn't wash because"it's too tiring" doesn't go out except to medical appts. He's made the situation worse by being so inactive that his leg muscles are wasting, and he's been told that is nothing to do with his illness, that's on him. When the healthcare professionals visit him, he acts all enthusiastic about all their suggestions, e.g going for a short, slow daily walk & building it up gradually, (He's been told to try that years ago but never has) but when they're gone he just doesn't do any of it. Then when they ring up to check on his progress he won't speak to them, but wants my relative to do it, and LIE and say he's been doing it 😡shee refuses to lie for him, thankfully)
I get so cross, and so sorry for my relative. She had a heart attack about ten years ago & had to be resuscitated-she nearly died and the family though this is the thing that will really wake him up and make him change, as he was absolutely beside himself with worry and he wasn't so bad then, he could help around the house and with meals etc. And he did change, for about a week. Then he just lapsed straight back into being pathetic again! She feels resentful because she knows their life needn't have become like this. But then she feels guilty.They used to love holidays and now she's finally retired early,they can't go anywhere or do anything together because he's allowed himself to get so bad. She can't even go anywhere with anyone else, because he relies on her so much. He was told years ago that if he followed the professionals advice, there was no reason he wouldn't still be able to go out on day trips and on holidays, even abroad, for years. But none of it's possible now.
So, in my opinion the OP should go. She's had years of looking after someone who could have helped themselves to mitigate their health problems, but didn't and now, like my relative, it's ruining her life as well as his own. As my relative says, it's not that he became ill that she resents, because that's marriage, in sickness and in health etc etc. If he had a condition that he could do nothing about, she'd care for him and accept it. The resentment comes from knowing it needn't have been this way if only he'd done something about it.