After Dr. Methuselah's wife, Candy, died, he went a little crazy. A little mean, a little maudlin. He mixed the genes of a weeping willow with a few DNA strands harvested from the hair of his late wife, weaving in a passel o' nanotech...
The first love tree seeded itself on top of Candy's grave. Satisfied, Dr. Methuselah killed himself.
The tree grew tall and lovely, with long limbs and leaves of peaceful sussuruss. And, after the course of a few seasons, it came to bear the most unusual nuts, the exterior of which resembled hazelnuts, spiny and vicious. The nut, however, was the color of brass, and hinged. Upon opening the nut, one would find a membrane, delicately balanced, that would always point true -- toward the holder's true love.
Some called the tree a blessing; others, a menace. But always the membrane would point toward the true love. Marriage, death, gender -- these things meant nothing. There was only the direction, and the courage to follow it.