Brain Damage.
When my father-in-law went down this path we are all witnessing, I had to convince everyone that this was a fact. They kept trying to either rationalize his actions or try to steer them. Tried to make sense of it all. That he’d get better.
“He’s brain damaged,” I’d say, “The MRI showed it.”
All we can do is keep him happy and not be a danger to himself or others. Take away the keys, put blocks on the windows, slides on the doors he can’t figure out, behind a door with a keypad. Drive him around the neighborhood now and again. Listen to the rambling stories. Put some meds in his apple pie.
It’s time to just admit it.