How do you know when to give up - on a sick kitty

As long as the cat is not in pain and has quality of life and you are willing to keep up your efforts. I applaud your efforts-not many people willing to go to that effort with a cat when there are so many people that despise them. We have a diabetic cat we have to give insulin shots to twice daily and a dog with Cushing's disease. Both doing very well but it does take effort and money. Worth it to me because they have a good life and they make me happy. But if they start to suffer and no way to fix it we will have them put down. Just a thought about the pill, can you get that in liquid or compound it yourself into a liquid? In my experience cats seem to do much better with the liquid in an eyedropper to the corner of their mouth than a pill forced down them. Might be a little less traumatic for him.