It existed between Adam and Eve. It was what Greeks call 'eros', a romantic attachment of one sex for the other. And since then, every one worth his/her heart has fallen prey to Cupid's arrow at some point of time.
When someone whispers 'I love you' in your ears or when eyes meet eyes, the tumult that it generates is more powerful than the sea in spate. It is a unique feeling of bliss and agony. If your lover or beloved is with you, it seems you have conquered the world. If he/she is away from you, the time becomes a burden. Lysander in Shakespeare's play "A Midsummer Night's Dream" aptly sums up, "the course of true love never did run smooth." (1.1.134).
I mean, that my heart unto yours [is] knit, So that but one heart we can/ make if it; Two bosoms interchained with an oath, So then two bosoms and/ single troth. Then by your side no bed-room me deny; For lying so,/ Hermia, I do not lie" - (A Midsummer Night's Dream. 2.2.47-52).
Romantic love defies logic. He/she may not be beautiful in others' eyes, but beauty lies in the eyes of the beholder. He/she may not have the best of qualities, but love-interest becomes the most ideal person. That is why love is said to be blind.
When Romantic love transcends physical barrier and turns metaphysical, it becomes Platonic. The feeling here is much different from what one gets in Romantic attachment. It is a kind of intellectual bonding between two friends. The feelings of jealousy and pining so common in Romantic love are missing here. In Shakespeare's play "Hamlet", the protagonist's bond with his best friend Horatio is the finest example of platonic love.
Plato put philosophy in love. The beauty of the moon or the twilight of sunset too evokes feelings in us. This is Platonic love. As William Wordsworth in "Ode on Intimations of Immortality from Recollections of Early Childhood," said:
To me the meanest flower that blows can give
Thoughts that do often lie too deep for tears.
Spenser's "Hymn in Honor of Beauty," Shelley's "Hymn to Intellectual Beauty," and Wordsworth's "Ode on Intimations of Immortality from Recollections of Early Childhood" express Platonic Love.
Attachment and affection are but the manifestations of love. These are best manifested in familial love or what Greeks called 'storge.' Familial love is self-less. Parents care for their offspring unconditionally. We love our parents for what they are and what they have done for us. A motherly caress soothes the worst of pains. A child looks up to his/her father as a pillar of support, a tower of strength and an ideal person to emulate. When a father places a goodnight kiss on the forehead of his daughter who has fallen asleep in his arms,