Hello DarkPira7e,
That's a shame your pet cat is sick -
Over the years, we have had several pet cats. My wife and kids and grandchildren get quite attached to them.
When one of our cats gets injured or sick, I'll care for it, to an extent. The extent usually ends when it has to go to the vet.
Back in the day, when the animal wasn't recovering and went off feed and was in pain, I would take it down to the woods, along with a hammer and then give it a proper burial. I would tell the family that the cat died and I buried it.
Today, I would take the cat to the vet to get a second opinion and if the vet said it was terminal (read - cost too much to make well), I'd pay the vet to send it off to kitty heaven.
humfrz