Sucks, bud, my condolences.
Few years back, my family's cat was put down after seventeen long years. It was a pretty rough car ride to the vet, as my mom and sis couldn't bear to make the trip since our cat had made a pretty sudden turn for the worse after some medical issues, and she was pretty much beyond saving.
Still held her paw as the vet put that needle in, though.
No one in the family's had a pet since that day.