That's terrible TA.
I know how you feel. When my cat, Dr Livingston, got suddenly sick, I spent the next two weeks doing everything possible to save him, (ended up with a $9,600 vet bill, and never regreted it).... but we were unable to.
I was destroyed for weeks afterward, and I sometimes think of him, years later. He was my little buddy, used to ride around on my shoulders everywhere, even hiking or going to malls. He looked a bit like your cat also.
People can say what they want about the priority that different people put on pets.... and I've been through some terrible things that involved horrible suffering for human beings, so I recognize the difference in degrees; but when your pet is such a warm, loving part of your life, the pain of that loss can be shocking.
