I know this was a week ago...I'm so sorry to hear about your sick kitty. It is so hard to lose a beloved pet, especially one from childhood. To me they are family members.
I was really sad for a long time when our beautiful golden retriever (15 years old) had to be put down a few years ago. He had had a check up a few weeks before, the vet said he was doing great, then he got very weak and sick. I took him back in and he had cancer all through is body and they could not save him with an operation so he was put down during the surgery so he didn't have to suffer any longer. We got him when I was 12, and I had a really bad junior high experience and he was my best friend. He came to live with DH and I as soon as we bought a house, so he was "my" dog for the last 5 years of his life and was still one of my best friends and truly a joy in my life.
I do know how you feel. I hope your kitty pulled through and if not I'm very sorry for your loss. 
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