That has always been the problem with the writing for Cain and Moira. Once they were put back together the writers obviously didn't have a clue what to do with them. We now have the same plot driven nonsense that we went through with Kate Oates, there is no character development they simply change the characters personality to suit the plot. It's lazy writing.
After last nights ep I am thinking that maybe the whole reason for this storyline was not to give Cain a new son but to resurrect 'bad' Cain - yawn.