btdt...sadly I'm another grey mom who has had to make this painful choice. My first greyhound was still running and going on lots of hikes. But she had a tumour in her stomach and couldn't keep food down. We knew her disease was terminal, and how we did not want her to be hungry, so we let her go. I still remember driving to the vet's office and thinking how normal we must look because she was standing in the back looking out the window like she always did on car rides. We made the decision about 24 hours after diagnosis; we didn't want her to feel any pain, and like many others, I'd rather say goodbye before they suffer because of how much we love them.
I'm wishing you all the best as tears run down my cheeks, because I know this journey is very long and painful.