This chap, Schopenhauer, wrote The World as Will and Idea. In this masterwork there is one chapter of just over three pages on The Metaphysics of Sexual Love.
Schopenhauer on love:
It is the ultimate goal of almost all human endeavour, exerts an adverse influence on the most important affairs, interrupts the most serious business at any hour, sometimes for a while confuses even the greatest minds, does not hesitate with its trumpery to disrupt the negotiations of statesmen and the research of scholars, has the knack of slipping its love letters and ringlets even into ministerial portfolios and philosophical manuscripts.
For illustrative example see Bill Clinton.
What is love?
what is manifested in consciousness as a sexual impulse to a specific individual is in itself the will to live as a quite specific individual.
whenever two people fall in love, however objective and touched even by the sublime their admiration may seem, nature’s sole intention is the procreation of an individual of specific qualities.
The true purpose behind the whole love story - although the parties concerned do not know it - is the production of this particular child.
The increasing affection between two lovers is, even now, really the will to life of the new individual which they can and would like to engender. From the moment when their eyes meet with longing, this new life is kindled, and it announces itself as a future individuality, harmoniously and well integrated.