I was worried about that same thing, them having Ben as Dean's son. But that has changed after this weeks episode. Ruby told Dean that he would become a demon when he went to hell. Eventually they all become demons. And the promo for next week showed Dean with the black eyes. So I think that Ruby telling him what he would become, and then him dreaming about himself as the one thing he hates most, that is what is going to make him fight like hell not to have it happen.