You know, I think you're right. Maybe Gwen's not making calf-eyes at him. Maybe ... she starting to catch on. She seems to be the insightful, instinctive one of the group. That there's really not much of a heart in there. Or rather, that he hasn't allowed it to touch him in a long time. (I think in a lot of ways, the reason Jack and the Doctor got along so well was because they were so similar in that respect. The difference? The doctor allowed himself to love (we think :)) ... Jack just can't allow himself to do that (or at least, doesn't seem to have in the last 40 years or so). So he has sex instead. And lots of it. ;))