Sweety, it's time to forgive yourself. There's really nothing to forgive here sugar. It's easy to say I guess, but it's true. Unless you were dragging Winston down the street, or making him treadmill, you've nothing to regret. As far as medical goes, shoot I spent a pile on my Red Dog, and the vet had no idea. Of course I refused to let them slice and dice on her either, and charge me thousands of dollars for a diagnosis a ditch-digger could have made. Dog was old, all used up, we worked and played hard, and it probably cost her a couple of years. I don't let it bother me at all, she was WAY above average for her breed, and she made it an average amount of time.
The Pope of Dogs absolves you of any guilt.