I think the flashbacks are so that you feel sorry for Bill and forget he raped and cannibalized Sookie in the back of a van. (He raped her in the show, right? I can only remember that he did in the book. He definitely violently attacked her in the show) They want to end the series with them getting back together without too much uproar, because, you know, he lied and stalked and then attacked Sookie! He is being painted as this family man, who saves slaves, and is basically a saint to gently wash away the memories of the psycho from the van.