So sorry to hear this. Pets are family, and losing one can hurt just as much as losing a human family member. I know that the two dogs I've lost still feel like profound losses in my life, even years later.
Lady Kat lived a good, long life though, and I hope that is some small comfort. I grew up with a cat also named Kat. I found him under a car as a kitten, abandoned, when I was a middle schooler, and he lived to be 21 before passing away a few years ago.
I am constantly amazed by the gifts that animals give us. A person once asked me, while she was struggling with her sick dog: "why does it hurt so much?" My response (in one of my wisest moments EVER) was: "Pets embody the best qualities of all of the people who are most dear to us, but without any of the worst qualities."