family members with dementia

My great grandmother passed away over a year ago. she was 92 and in perfect health before the strokes that killed her. after she passed my great grandfather who's 99 now went down hill fast. he didn't need to be alone. so my husband and I had him live with us. it's so hard though. I didn't ever imagine it being this difficult. he has sitters from 7am to 7pm so he's never home alone. but having strangers in my house every morning before I wake up is getting stressful. on top of that my grandfather is practically a stranger to me now in his state of mind. he doesn't act the same at all. he has no idea who anyone. what year or day it is. even simple objects he has forgot the names of. what is the point of living when they are this far gone. he says all the time he'd rather be dead than sit around all day knowing nothing. due to him being confused all the time he's upset a lot! never wants to bathe and barely eats. I feel like it's so unfair to him to have to live like this.