I do want to reassure you that feeling overwhelmed in this situation is not unusual in caring for someone with dementia. Your history with him complicates things further however, it must be hard to know whether nastiness is the dementia or just him. I do feel what you have written about your past with him that it has been emotional abuse, and possibly financial too (he was quick to call you a loser when you lost your job).

I am reading that you are staying with him mainly because you fear without you there his care package will not be sufficient, is that fair to say?

I think that is not a positve reason to stay, it sounds like guilt but you do not owe him your life - it sounds like he has not always been supportive of you.

He may well fare better than you think in a care facility. You could still be part of his life just not providing the level of support care and planning you have done. It does not have to be the awful scenario you fear.