Outside of any pre-existing MH concerns I think anyone would be struggling with the situation you are describing.

I have written this before but the emotional rollercoaster you describe is one I have seen many care-givers of people who have dementia go through. It is an extremely hard experience exactly because of the love you have for the person who is going through these changes in behaviour.

You deserve and need all the support you can get - if you can seek out an in person support group for care-givers of those with dementia in your area while he is cared for at this time that would probably be very helpful.