Very sad to read this. I went through the same kind of situation a year or so ago, with my ex's cat Pebbles who became my most loyal friend, and stayed with me when we split up. She would, quite literally, talk to me with her sqwauks and miaows - the cat people will know what I'm talking about
It was the most heart-breaking thing to do, taking her to the vets that night, they're 10 minutes walk away so I just carried her down, and talked to her all the way.
But you know what? Reading this has made me realise that I want another cat now. To feel the lows you've got to have had the highs.
(EDIT - first post! so, hello all
))