It could be, rather, that the strain of this situation is starting to show on Park? Make is seem normal if you like but I don't know of any relationship where one partner comes back from a trip and cannot wait to be reunited with their mate. The situation of knowing your partner is fucking someone else causes deep internal psychological reaction that is observable to some. The first sign of distress is the look on Park's face. The second sign is that he will, more and more, begin to reject sexual advances from Caroline. Ask me how I know.