I feel for you bro! I'm a dog lover myself.

This is always the toughest decision, but to keep the dog alive is sometimes being selfish, we want the dog to live as long as possible, but living and suffering are two very different things.
14 years is a long time for a dog, and has probably had a good last 9 years.
If the dog is truly suffering , then you have to do the right thing for the dog.
My friend gives his dog the glucosamine for his back legs and it seems to be helping, I don't know about the eye? but I wouldn't put a dog down just because it has one bad eye! It can live with one eye quite comfortably.but if the arthritis gets bad in the legs
then the dog will be suffering.
I had to put my last dog down at the age of 4, she was epyleptic
and the medication got her so relaxed she would pee on the carpet without even knowing it, that wasn't quality of life, and that's what counts, niot quantity!JMO bro! I know it's tough.