It sounds like you really were trying your very best to help your cat. I am so sorry to hear how much you are in pain, and I understand. I had to put my cat down about 8 years ago and I still cry over her because I miss her and feel horrible about when she died (she got very depressed when I went to university, and it felt like I had abandoned her when I really hadn't wanted to.... she went downhill quickly and I had to put her down because my parents pretty much made me... and knew she was hanging out JUST for the chance to see me... and then the vet didn't give her enough of the drug and I had to sit there with my cat paralyzed for ages. It was... traumatic. So I understand.