soul mate

soul mate
    n 1: someone for whom you have a deep affinity
    

49 Moby Thesaurus words for "soul mate":
      Antony and Cleopatra, Pelleas and Melisande, Romeo and Juliet,
      Tristan and Isolde, ally, alter ego, analogon, analogue, associate,
      bill-and-cooers, brother, close copy, close match, cognate,
      companion, complement, congenator, congener, coordinate, correlate,
      correlative, correspondent, counterpart, equivalent, fellow, image,
      kindred spirit, like, likeness, lovebirds, mate, near duplicate,
      obverse, parallel, pendant, picture, reciprocal, second self,
      similitude, simulacrum, sister, soul mates, such, suchlike, tally,
      the like of, the likes of, turtledoves, twin