Anguish of romantic rejection may be linked to stimulation of areas of brain related to motivation, reward and addiction:
""This brain imaging study of individuals who were still 'in love' with their rejecter supplies further evidence that the passion of 'romantic love' is a goal-oriented motivation state rather than a specific emotion" the researchers concluded, noting that brain imaging showed some similarities between romantic rejection and cocaine craving. "The findings are consistent with the hypothesis that romantic love is a specific form of addiction."

To paraphrase Mr. Robert Palmer, you might as well face it, you really ARE addicted to love!