I feel your pain my fellow steemian.
My father was diagnosed with both Alzheimers and Dementia at the age of 66.
He was also a genius and chose the lifelong field of running data processing centers.
Since he was divorced and I was his only child it was a very terrible journey for the two of us, especially when I had to place him in a secured facility.
He would have many periods of perfect clarity, begging me to not take him back where I had him or calling me at all hours pleading to be picked up, then the dementia introduced an abusive side of him like I had never seen from anyone, especially my loving father. He passed three years later.
I'm so sorry to hear of your loss, and the long ordeal you both suffered. Of course the worst part for me was losing the person I knew even before he died.
Definitely the most slow painful part of the disease.