When I was ten years old, our cat, Boots, was put to sleep. I had known him my entire life (he died at the age of 22!), and I was unbelievably sad and depressed for a couple of days. However, he was really miserable. He was blind, cried all night, and only weighed about 5 pounds. He just wasn't happy. It was a very hard decision, but looking back, it was the best we could have done for him
Also, our cat, Neco died when I was three. She had leukemia, and was 15 at the time. She was put to sleep, but my parents didn't tell my sister or I until after it had already been done. I still resent that.
Thinking about our two old cats has already started getting tears in my eyes....excuse me for a moment....