Perhaps because the origins of a certain kind of love lie in an impulse to escape ourselves and out weaknesses by an alliance with the beautiful and noble. But if the loved ones love us back, we are forced to return to ourselves, and are hence reminded of the things that had driven us into love in the first place. Perhaps it was not love we wanted after all, perhaps it was simply someone in whom to believe, but how can we continue to believe the the beloved now that they believe in us?