SRS,
I have four cats and I love them dearly. I also can not have carpeting, clean the bathtub daily because Alice prefers it to the litter box, clean the litter box and basement floor daily because Ed prefers the basement floor. They snarl, spit and fight constantly. Each has rituals to start and end the day and it takes me an extra half hour in the morning to get dressed or I come home to cat vomit. Like I said, I love them dearly and enjoy the nighttime cuddles. But I loof forward to a day when I am down to one "normal" cat and a life. And then none.
I keep telling thm I am going to replace them with a goldfish and if he is a problem I will flush him.
Keeping an unhappy pet alive out of guilt is just wrong. He was suffering and so were you. I wish the same end were available to us when illness and pain can not be cured or relieved.
You did the right thing. Your son will see that in time, maybe when he has to make the same decision.
RIP, Kitty.