Awww, I am so sorry. that is such a huge fear of mine. When I was a child, our cat got out and although I didn't see it, I heard it as I was putting my shoes on to go catch her. Seeing her is an image I can't get out of my head but you do move on and the pain does lessen. I agree with talking to a priest, rabbi, animal loving friend. Try not to blame yourself, it was an accident and dogs just dont have the sense to stay out of the road.