Origin of the Word:
As you might expect, love is almost as old as time. The word’s ancient root is also the source of Latin lubido ‘desire’ (which gave us libido (early 20th century)). Love is blind goes back to classical times, but first appeared in English in Geoffrey Chaucer’s Canterbury Tales in the 14th century. Lewis Carroll appears to have been the first to use love makes the world go round, in Alice’s Adventures in Wonderland in 1865—he may have based it on a French folk song with the lines c’est l’amour, l’amour, l’amour, Qui fait la monde à la ronde, ‘it is love, love, love that makes the world go round’. In 1967 the Beatles sang ‘All You Need is Love’, and a slogan associated with the weepie film Love Story ( 1970) was ‘Love means never having to say you’re sorry’. The love that dare not speak its name is homosexuality. The description is by the poet Lord Alfred Douglas, whose association with Oscar Wilde led to Wilde being imprisoned in Reading gaol for homosexual activity.The use of love in tennis and squash for a score of zero apparently derives from the phrase toplay for love, that is for the love of the game, not for money. A popular explanation connects it with French l’oeuf ‘egg’, from the resemblance in shape between an egg and a zero ( see also duck). One caricature of actors is that they all gushingly call each other ‘love’. In the late 20th century an actor, or anyone actively involved in entertainment, came to be a luvvy, a respelling of lovey, an affectionate term of address used since the mid 18th century. 
C. S. Lewis in The Four Loves:
To love at all is to be vulnerable. Love anything and your heart will be wrung and possibly broken. If you want to make sure of keeping it intact you must give it to no one, not even an animal. Wrap it carefully round with hobbies and little luxuries; avoid all entanglements. Lock it up safe in the casket or coffin of your selfishness. But in that casket, safe, dark, motionless, airless, it will change. It will not be broken; it will become unbreakable, impenetrable, irredeemable. To love is to be vulnerable.
Alone among unsympathetic companions, I hold certain views and standards timidly, half ashamed to avow them and half doubtful if they can after all be right. Put me back among my Friends and in half an hour – in ten minutes – these same views and standards become once more indisputable. The opinion of this little circle, while I am in it, outweighs that of a thousand outsiders: as Friendship strengthens, it will do this even when my Friends are far away. For we all wish to be judged by our peers, by the men “after our own heart.” Only they really know our mind and only they judge it by standards we fully acknowledge. Theirs is the praise we really covet and the blame we really dread.
I love you in other languages:
French: Je t’aime
German: Ich liebe dich
Latin: Te amo; Vos amo; Amo te
Russian: я люблю тебя (ya lyublyu tyebya)
Spanish: Te amo; te quiero
Link to psychology today article on the science behind love: https://www.psychologytoday.com/blog/loves-evolver/201302/the-science-behind-falling-in-love
Some Latin phrases concerning love (amor):
Amor patriae: Love of country
Amor nummi: Love of money
Amor proximi: Love of one’s neighbor
Amor vincit omnia: Love conquers all
According to Elizabeth Hanes (history.com):
Chaucer may have invented Valentine’s Day.
The medieval English poet Geoffrey Chaucer often took liberties with history, placing his poetic characters into fictitious historical contexts that he represented as real. No record exists of romantic celebrations on Valentine’s Day prior to a poem Chaucer wrote around 1375. In his work “Parliament of Foules,” he links a tradition of courtly love with the celebration of St. Valentine’s feast day–an association that didn’t exist until after his poem received widespread attention. The poem refers to February 14 as the day birds (and humans) come together to find a mate. When Chaucer wrote, “For this was sent on Seynt Valentyne’s day / Whan every foul cometh ther to choose his mate,” he may have invented the holiday we know today. 
Sources:  http://www.oxforddictionaries.com/definition/english/love?searchDictCode=all