I’m so sorry. We had to have our wonderful black Lab put to sleep in Narch, and I am still not over it. I know how you feel.
I have to jump in with advice here. It is better for the dog to end its suffering sooner rather than let it linger in pain. First, dogs are stoic. A dog will suffer great pain in silence, and chemo is miserable. People understand it is done to prolong life. A dog just knows it is being put throug a painful ordeal.
Then there is the consideration of the dog’s dignity. Yes, dogs have it, and you don’t want your dog to go through the humiliation of being too weak to move or of becoming incontinent.
Although I know it would be horrible for you, you have to think of what is best for your beloved pup. There is an excellent piece online called When to Let Your Lab go. He says sooner rather than later, and I agree.
I am saddened that people are doing hospice for pets. That is merely increasing their suffering. A pet has no affairs to get in order or spiritual concerns.
There is a greater incidence of cancer in pets, but it is because more of them are living into old age when cancer is more common, just as it is in people.
I will say a prayer for you. Losing a wonderful pet is so hard.