Difficult to handle the daily roller coaster of Mom's dementia. One minute she thanks me for all I do, the next minute she says I never visit her a drink of nectar when I spend about 6 hours daily making sure she gets her drinks, some food, demand the aides do a brief change and/or offer bedpan every 2 hours, I clean her mouth and teeth almost every morning, play comforting music, calm her when she is in a "spell" of not responding for an hour or two. Then one day she has a great day, joking, eating a little, etc.
I'm not trying to criticize, but to give you permission to "neglect" her a bit so you don't "neglect" him so much. You know what's best for your situation.
I found it really helps to talk to other who understand. This is a great site for sharing experiences. I also found a local support group very, very helpful.