Dejibo,

House cats often die of high output kidney failure. They pee so much they are thirsty and dehydrated. The next step is subcutaneous fluids several times a day that Jack would not like.

Having watched one cat go through this and die on her own grating her teeth and then putting the next two to sleep before they got to that point, I think it's time.

I sympathize. It's a very personal and difficult decision.
ANN