We can tell you that you have been in this situation with him before in another life, but the shoe was on the other foot. You were the one in decline and he was the caregiver but did so unevenly in the mistaken assumption you were oblivious and nothing he might do to assist you would have any meaning you could perceive. So the current situation is to have him experience what you went through in being at the mercy of his perceptions and choices that led to some neglect. You have an opportunity now through loving kindness to heal the karmic wounds from what happened before, and this will help the both of you heal, once and for all, the karmic wounds. This may or may not bring about any noticeable improvement in his dementia but it will free you both from having to repeat yet again this dilemma on either of your parts, and that would be a tremendous benefit indeed.