Sorry to hear that. I disagree though with killing sick pets. I think it is inhumane to animals and you should treat them like you would people. Would you kill a sick relative with a lethal injection for a crime they didn't commit?
Yacov, there are times when the animal simply can not be cured, and allowing them to go on living would be cruelty. There are also times when the animal is dying, but dying a slow, painful death. It's better for the animal to have a way out.
The first dog we put to sleep had severe pneumonia. I wore myself out carrying her around trying to get her into a steamy bathroom, trying to coax her to take medication that she was refusing to take, even hidden inside food, and trying to sleep in the short bursts between her coughing fits. She was getting worse and worse, and slowly drowning to death, even though I fought hard for weeks to try to save her. There was nothing else to do, and she kept looking at me with this expression like she was in a lot of pain, and the coughing got worse and worse. I basically got no good sleep for a few weeks, because she was constantly coughing and had to be positioned upright and patted on her side or put into a steamy bathroom to help calm the fits, which would only work for a very short time, an hour or two at the most. I was about to drive my own health into the ground for her, and she was only getting worse and worse and worse. She was also elderly and had had a string of health problems over the last year, as if her body were trying to shut down. We really had no other choice, for her sake. I wasn't going to allow my little girl to drown to death inside her own lungs, because she was quickly headed that way.
The other two times were just as obvious and there was no other choice. I prayed that they'd die peacefully in their sleep so I wouldn't have to do that, because believe me, it's very painful to have to make that choice. After that first time, I wasn't right for a whole year afterward. The emotional toll was horrible.
Yacov it's not something people want to do, but it's often the only humane choice.