My sincerest condolences.
Here's my story...I worked as a veterinary technician for several years after high school. I have euthanised or assisted in the euthanisation of at least 100 animals, probably more. All were necessary, and none were easy.
My own cat, Peje, died at age 7 from acute renal failure of unknown etiology. He was fine one day, vomiting and lethargic the next, and less than four days after the initial diagnosis, we had to euthanise him. I assisted; I held off the vein, bagged the body, and made the crematory arrangements. I picked up the urn, paid the bill, and did it all without a tear. Three weeks later, I was sitting on my sofa and looked down to find a cat hair (his) stuck on my sweater. I couldn't stop sobbing for two hours