Tracy, you will know and when he gives that 'ok' to let him go, it will ease your feeling of guilt. No one should feel quilty for letting a pet go, pain, yes, but not quilt. My hardest furkid to have put down was Lacey, because she wasn't really sick, just couldn't walk. My vet told me that was in a sense, sick. She had little quality of life left when she couldn't even walk the yard a bit and then couldn't get up and falling all the time. I swear, at the vets, she was hoping that's why she was there. She seemed so tired of all of it that day.
I am keeping you, your family and Scruff in my thoughts and prayers. {{{hugs}}}