In the development of mankind as a whole, just as in individuals, love alone acts as the civilizing factor in the sense that it brings a change from egoism to altruism.
Sigmund FreudLet us consider the polarity of love and hate.... Now, clinical observation shows not only that love is with unexpected regularityaccompanied by hate (ambivalence), and not only that in human relationships hate is frequently a forerunner of love, but also that in many circumstances hate changes into love and love into hate.
Sigmund Freud