The balance

With this concept i would like to explore the ideas of pairs. I think there is an odd intangible factor that brings out the connection or bond between certain things that just go together. For example a spoon and a fork, could we not just use Sporks? Why is there necessity in pairs and why do we seek relationships? What is the human bond that ties a boy and a girl together, is it the emotion, love or hate? or is it a mental need and bond.  I'd like to look at parallels which cannot go without each other, for example life and death or love and hate.