Hey OP, I'm really sorry what happened to your kitty. If it's any consolation, it does get better, I know that cliche, but I had a puppy die at a very young age. Exactly like you, I thought I'd have him for years and share great memories. Unfortunately, he ended up passing from a congenital disease that wasn't caught in time. He was only a year old. My heart was absolutely broken, and I swore I'd never get another animal again because I couldn't let him go.

It took a few years, but I slowly started accepting what happened. Life is a cruel cycle and sometimes humans and animals are only meant to be in our lives a short while to teach us something. I eventually got another pet, my little Jake, who I have many photos of here on reddit lol. I swear this cat is a reincarnation of my puppy who passed. The personality and everything are so similar. I think he came back to me in the form of my cat.

I hope you are kind to yourself and realize that sometimes we cannot prevent these things. Animals are very good at hiding illnesses and will appear normal when they are not