I have never been in a situation where I had to make this kind of dissension and I pray I never will be. It's so hard to determination when its time you should say your good byes.
Have you spoken to your vet, i would follow my vets advise.
The last gift of love we can give our fur babies is the gift to end their pain.
It's all about quality of life.
I am so sorry you have to go through this
Speak to your vet