Oh Luckygirl what a terrible situation for you to be in, I'm so very sorry
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Have you found somewhere suitable for him to go?
When my step father's vascular dementia was getting to the point where we knew he would have to go into full time residential care, we arranged for him to go one day a week for a couple of weeks and then for two.
We did feel that that helped him to accept the change when he needed to be there full time. Not knowing what your OH's problems are, I don't know if that would make it easier for him and you too.
I cannot begin to imagine how heartbreaking this must be for you but if even with live-in assistance his care is becoming more than you can handle, for his sake and your own it seems you may have no choice.