Dark Harbor - what about the watches?

Hey folks, I've just re-watched Dark Harbor yesterday night and there's this scene shortly before the climax, when Alexis checks the time on David's watch. David seems kind of pissed of or even alarmed that she isn't wearing her own watch because she usually always wears it. Did you understand why she isn't wearing it or why this seemed to be a problem for David?
And shortly afterwards the unnamed young man says he likes David's watch. There has to be a special meaning behind this statement, hasn't it? Can you help me there?