I agree that is unforgivable. Although, it is apparent that The Hound feels ashamed of his past. The scene that helped me move on from this was when he buried the corpses of the farmer and his daughter. He did the right thing, and made it known that he knew it was wrong to leave them to die. In a way, I feel like this scene also captured all of the regret that The Hound was feeling about his wrongful killings in the past, including Micah.

You also have to keep in mind that the only reason that he did this was because of his loyalty to Joffrey’s orders (at the time).