I loved my old dog... she was not blind nor deaf but had arthritis in her spine... she was incontinent, couldn't get up or lay down, and in constant pain (tried lots of meds but vet said there was nothing more we could do)
I had to have her put down...
Cried in the parking lot for a while before I could pull myself together and drive home...
I guess I'm saying that at some point you have to ask yourself what is life like for the dog.
Sorry if that seems harsh
I feel your pain.