We went through all of this. Finally, though he was already blind before we thought, all the sudden he acted like he was lost and was making noises and we knew he was in pain. Sorry to say he was misserable and the vet said he was suffering so this was the end of a 14 year happy life.
I still miss him though it will be a year in July.
Just make sure that he is not suffering, all the love we give them wil not take away the pain.
I will be thinking of you since it is a very diffcult time, but all the sudden you will find the answer what is the right thing to do and is the best for him.