I think John mayer tries to say to the girl he sings to that he doesn't know exactly in which situation their relationship is, maybe because sometimes he feels guilty about what he does with other girls or the opposite but they have never made things clear so, they both are in doubt but no one says anything because their pride is far too much stronger. And also he can't stop trying to find out how this girl's life is going on. So he watches her pictures from afar.