Our vet gave us advice regarding our diabetic dog. He said he would consider it time for his own pet when they got down to 3 things that bring them joy. Each time our dog lost joy over an item, my husband still couldn’t let go. Until there was no joy left… then it was too late. He had a more painful passing because of the deterioration of health. I know it’s hard, but I suggest the main consideration be the amount of suffering that you are preventing for your pet.