Beautiful post, Monica!
Floridagirl, I'm sorry about your illness. I really do think you should put yourself first now, unless doing things like volunteer work makes you happy. And yes, I see the irony between what many people say and how they react if you follow their advice.
Mumsyface, it differs from person to person, of course, but I think often elderly people seem to be more "self-centered" b/c they know for sure what they like/dislike and aren't as tolerant of situations that make them unhappy or uncomfortable. It may be partly the sense of the shortness of time they have left.
"... how does one deal with it?"
First, I think one deals w/ it by accepting the elderly person's limits to the extent possible. If they say, for example, "No, I'm not going to the family reunion this year," then accept it, don't argue and try to think of ways to get them to change their mind, etc. If they say, "I'm not going to GD's graduation," IMO, that's a little more serious. I would tell them that GD will be hurt (if she will), but then leave it up to them. If they insist on driving when they don't really drive well anymore, that's very serious, and I would have sit down to discuss it, and ask for the car keys, even if it were a very uncomfortable conversation.
These^^ are just examples, but do you see what I'm saying? IMO, there are different scenarios, and one has to handle them all accordingly. But, overall, I think we need to respect the older person's wishes, even if we don't agree, unless they are terribly dangerous.
Oh, but, we need to have our limits, too. Sometimes, we, also, need to say no, for their health or ours, even if they complain. As a PP said, much like dealing w/ a toddler.
I'm confident you can figure out how to cope w/ DH if that's what you're wondering. Best of luck!