I agree with HilaryB, and I suspect she is right about:
'Your husband may want you to be your usual happy self, but I doubt whether he really believes you can be'.
'Doing our best' is the best that any of us can do - looking back, you will probably think 'I could have done better' but in reality, we all learn things as we go along, and knowing that 'I could do it better now' does not mean 'I could have done it better then'.
'Going along with the wishes of a dying person' is, I think, almost always the way to go - the alternative, would be to argue with a dying loved-one, and personally arguing with, and 'upsetting', a dying loved-one, isn't anything I would be keen to do.
By the way, at the risk of appearing sexist: I gather (and I'm male - so this isn't something I'm going to understand !) that women are much more 'self-critical' than men, on the whole. Try to avoid being overly self-critical, if you are supporting a dying loved-one, or have supported a loved-one who has died: you will [I suspect] have enough regrets as it is, without unnecessarily adding more to the list.