Might have been someone else.
Thing is... We have seen softer sides of Chrissy. (maybe a couple of soft sides.) And she's not a bad person, just heavily insecure. Jack has to have some reason, aside from Charon's theory of child obligations to stay with her. Maybe when she's not ranting about Charon she can be a sweet person. After all, we haven't see lot of their homelife.
Or maybe she's just really dirty in the sack.
