I remember Nancy Reagan calling it “The Long Goodbye.”
It truly is.
I realized last Nov. that my sister no longer knew me and I said my last goodbye to her then.
I choose to remember how she was in happier times.
So sorry that you had to go through it with your dad.
For a while, at least, after a person with dementia no longer knows exactly who you are, they still know that you are special to them.