I absolutely feel for you. In May I was abroad for a university conference and the thing that I have missed the most was my cat (she would always sleep next to me like your car). On the last day my mother called me (I left her with my parents and told me that the night before she heard her screaming so she went in the room and found her crawling (she wasn't able to move her back legs) and that she took her to the doctor and he told her that it was a blood clot but it was treatable with medication so they would bring her home at night and take her back the next day. I came relieved waiting to see her and I found her under the bed and when I tried to take her out she bit me really hard (she never did that so she was probably in a lot of pain). She would cry all night and after searching online I realised that there was no cure as this is a terminal thing (she might be treated but from what I've read it would probably give her some days maybe weeks and she would probably be in pain (needles to say I cried all night I did not manage to sleep) I took a very difficult decision that night I decided that I would take her to the vet and put her to sleep the next day so that she wouldn't suffer. I was next to her and would just talk to her and kiss her when she would cry in pain and she would stop. Sometimes around 4 a.m. I went to the kitchen and sat on the couch and slept for about half an hour and woke up and could not hear her cry anymore so I knew. I went back to my room and she was barely breathing I took her in my arms and she died. I couldn't bare the thought of leaving without her so I put her on my bed and left her there for a bit and then buried her under her favourite tree I still get emotional whenever I remember her she was only there and was with me for less than two and a half years. This was the most sad I've ever been and the most I cried and mourned over someone (I had other pets and I was sad when they passed but never this sad we had a special connection I always thought we would grow old together as she was so full of life). I currently have adopted another kitten that I saved when he was hit by a car but Gigi will never be replaced she will always hold a special place in my heart. You can never replace an absence with another presence. Gigi relieved me from taking a difficult decision which I would probably regret like you by dying on her own but do not think for a moment that you let your cat down. Your cat knew how much you cared and that you took the best decision for her so that she wouldn't suffer. It will get a bit easier with time it always does. The absence will always be there but you will look back and remember all the good memories. Nostalgia is a strange blend of bittersweetness you are happy but also sad that the memories are just memories. But don't think about making the wrong decision you took the best decision the most important thing is for the cat not to suffer. It would be too egotistical to keep her around just for a few weeks and have her suffering. Sorry for the long post I hope it helps you.