Oh man, I'm really sorry for your loss.
I know very well how it feels to lose a pet, because two years ago a had to make a decision for my cat, Säkä. Säkä was a fine cat, he never was ill or anything like that, and we were all very fond of him. But one day, Säkä started to have seizures. It was horrible to watch him suffer, his seizures were so bad that he accidentaly tore almost all of his right paw's claws off, and nearly bite me when I tried to help him.
I took him to the vet at that same evening, the vet took x-rays, she suspected a tumour. But because of some malfunctioning, the pictures were blurry and she didn't know for sure. She gave Säkä some medication, which calmed him down a bit, and said that I'll should watch him for the night, and if the seizures continued, I should bring him back for the final journey. And they did continue.
I remember that I was crying the whole time I was with Säkä as he was put to sleep, and I still cry a bit when I think about those last moments.
Now I have two cats, Nappi and Neko. Nappi was at that time a year old, and after Säkä passed away, Nappi depressed. He wouldn't eat enough or play with us, just sit or sleep. Luckily, one of my friends were giving away her cat, who was seven months old, and we took him to us. Fortunately Nappi liked Neko immediately, and now they're like best friends.
Jam it back in, in the dark.