I had a cat a few years ago, it was a bit of a rascal really, but if you just looked in its direction it would purr. One day it went missing and two days after that it was lying on the lawn, barely alive as it had been knocked by a car whilst mousing over in the field opposite the house.
I was on the way out to an exam when I saw it, and I just cried and cried because it had smashed its jaw up real bad and was looking real bad - the poor thing must have crawled for days in pain to get back home. The poor thing tried to purr when it realised we'd found it, it was really heartwrenching seeing it that way.
God I was/am heartbroken. My mum took it to the vet, who said they'd be able to fix her up, it cost loads of money but it was worth it. The thing is though, about a year later it got hit again, fataly. They bloody bomb up and down our road in cars the bloody b*stards, its supposed to be 30mph but I dont think theres one which doesnt scream past at over 50-60mph.
My other cat didnt understand where the other had gone, and the whole thing was really upsetting. My cats are my little 'babies' and its really hard to come to terms when one dies. I agree with the above though, if its in real pain and suffering all the time and lifes really hard for it, then perhaps its in its best interest unfortunately.
I really feel for u m8. Its a real shame.
Sirius.