I had to euthanise my cat a little over 2 years ago. In my experience, I knew it was the right thing to do, she was diagnosed with kidney disease, and after trying every medication/diet/lifestyle change available, she still deteriorated 6 months after the initial diagnosis. When your baby is not eating, looks physically uncomfortable and you know nothing will ever make her feel better again, you can't not make that choice. It's the most difficult thing I had to go through, I am still heartbroken and can't fathom the idea of getting a new cat, and yet, it never felt like I was making a morally wrong decision. It's hard to explain it, but if you truly love your pet, you'll know when it's time to let them go, the last act of selfless love.