A) Because we all have a soul mate and the purpose of life is to find them.
B) Its nature’s way of ensuring that we reproduce.
C) It only exist for those who choose to believe in it.
D) We are all spirits that originate from the same shared consciousness (God, energy, whatever you want to call it) and the nature of that consciousness is pure love. Falling in love with another person is the easiest way to remind of us that, even if it is only on a deep level that we aren’t even aware of.