Napoleon and Josephine
Perhaps a testament to the beguiling effects of romantic indifference, Napoleon Bonaparte and Joséphine de Beauharnais loved each other dearly - yet never at the same time. In 1795, at the beginning of their affair, the general (as he then was) wrote to his beloved: "I awake full of you. Your image and the memory of last night's intoxicating pleasures has left no rest to my senses." However, not only did Josephine fail to reciprocate his ardour, sending few letters in return and initially refusing his proposal of marriage; she also cuckolded Napoleon with a dashing lieutenant months after the pair wed in 1796. Distraught, Napoleon vowed never to allow a woman to hurt him again, stating that Josephine had killed his heart.
On learning that her indiscretions had been discovered, Josephine realised what she had lost, and fell deeply in love with her husband. Sadly for her, though the couple remained married, it was too late to salvage their relationship.
Napoleon never felt the same towards her and, though she remained faithful, he took many mistresses, finally divorcing Josephine when she failed to produce an heir. But although he remarried, Napoleon never truly fell in love again. Which is, when you think about it, quite romantic.