I don't know, I think Ben and Carrie Stokes is kind of "EWWW! Yuck!"
Given that Roger turned out to have been married to HIS grandmother
, and they even had a child
, it wouldn't be unheard-of on DS. Incestors after all. But he had a valid excuse. He didn't know, and nobody bothered to tell him later.
It would have been impossible to pull that off with Ben and Carrie, since they knew each other all her life. Maybe in Parallel Time ?