We put one of the cats down last night. He was fifteen years old (which is a full life for a cat), and he'd been adopted by The Beautiful Woman back when he was a kitten, in the days when we just dating (and still professing that it was just a fling and would never go anywhere). When we took him in to the vet today, he was little more than skin and bones, except for his abdomen; his abdomen was little more than tumor. He was still eating, and still drinking his water, but he'd started having trouble getting up and down from things... or even standing up, sometimes. He'd also started... not quite meowing, but making a sort of puzzled mew that suggested that he was kind of uncomfortable and wasn't entirely sure why.
I never know how to call these things. I don't think anybody does. We could maybe have kept him alive longer than we did (but you never know). On the other hand, I think he would have been sliding from "uncomfortable" to "miserable" by imperceptibly tiny degrees (but you never know). Or he might have gone a few more days and then keeled over on his own (but you never know).
I do know that he spent the last two months eating wet cat food and being fussed over, both of which he very much enjoyed. I know he snuggled with my wife and the boys, and that a lot of what our boys know about how to treat animals they learned through him. For all that cats are supposed to be imperious and indifferent, he was very much an affectionate and involved member of the family. He will definitely be missed.
We've done the best we could for him. I hope we've done right.