My grandpa passed away long time ago.
I was a child back then, I didn't know what a neurodegenerative disease was at that time. I just notice it on him first. (He strugled with Alzheimer too) 
Things evolved very gradually. I have memories from when I was 7  telling him the same thing twice and noticeing the same reaction like it was the first time he heard me telling it. 

For the last half a year of he's life he recognise only 2 things: my grandma and the house (only inside and the front of. eveything else  was a complete mistery) He become so slow in moving and thinking that actually one second for him was like 1 minute "on  planet earth" (the famous time meme).
I remember watching him and asking deep within myself " what a life is this ? is it still "living" at this point ?" (I was 13)

It's hard to let go, Take care 🫂🫂