His regular vet called me on Thursday when she got the records from the emergency vets office. She was so kind and assured me that I did nothing wrong. I told her I felt like I failed him and she said that he just had poor genetics (as he has had other ailments since I got him as a kitten), and it was just his time. I keep thinking I see him and it startles me. I am trying to keep busy with other things though, which helps, although mornings are the hardest as we had our routine.
When I lost my cat, Dino, I heard him for a couple of years after that. I would hear his little cry in the distance. It was strange and soothing at the same time. He was a rescue and I think his mom was feral so he had multiple issues, too. I gave him his best life and he gave me unconditional love.