Please don't beat up on yourself. Try to turn it around and think of it as a fostering and learning experience for Ace as well as you and your wife. Ace is now more used to a home and knows how to relate to people in that environment, the group will know to place him in a home where his separation anxiety will be managed, and you have learned that you need a different type of greyhound -- and they are all different. I had one with such bad SA that she ate through the walls, tried the metal door, cried, etc. Yet she was the star of her therapy dog class and then graduated to an in-home therapy arrangement which was a harder test to pass. My girl now HATES walking, has no idea why I want her to do it. Both were learning curves for me but now I have the tools to deal with the situations. That is what you have given yourself, knowledge of what you can and can't deal with and how to deal with it. Just remember, if you see Ace again, he will be happy to see you and that is what matters most. You helped him to be ready for his forever home.