There's a lot of version that explain where do this Valentine's day started to be celebrated. Allow me to quote several version that I got from wikipedia.
The first representation of Saint Valentine appeared in the Nuremberg Chronicle, (1493); alongside the woodcut portrait of Valentine the text states that he was a Roman priest martyred during the reign of Claudius II, known as Claudius Gothicus. He was arrested and imprisoned upon being caught marrying Christian couples and otherwise aiding Christians who were at the time being persecuted by Claudius in Rome. Helping Christians at this time was considered a crime. Claudius took a liking to this prisoner -- until Valentinus tried to convert the Emperor -- whereupon this priest was condemned to death.
That's the familiar version that I read in some magazine. Here's another version of St. Valentine history.
English eighteenth-century antiquarians Alban Butler and Francis Douce, noting the obscurity of Saint Valentine's identity, suggested that Valentine's Day was created as an attempt to supersede the pagan holiday of Lupercalia. This idea has lately been contested by Professor Jack Oruch of the University of Kansas. Many of the current legends that characterise Saint Valentine were invented in the fourteenth century in England, notably by Geoffrey Chaucer and his circle, when the feast day of February 14 first became associated with romantic love.
See? There's no such kind of history's here mentioned anything about 'love'. Only the one above that say something about marrying the Christian and so he was beheaded because of it. That kind of bloody history and uncertain line of history really is interesting, right? I don't care. From my opinion, it's only the engineering of the merchant. Specially candies, chocolate, flowers, and everything that got to do with the color pink merchant. Do you know what the love symbol means? That love shape? It's your heart. Wait, let me show you the picture :
This is a love symbol. Looks cute, huh?
This is our heart organ. Feel familiar? It's been re-shape to a very cute love symbol as we know now. Some people may found this utterly cute and by giving out the love symbol means that you're giving out your heart to them. Well, I call this crap. Lol.
So this is me. I don't like crappy romantic things that is not realistic. Honestly, I think that 'love' which those teens keep saying to their couple is only a justification of what they're going to do with their couple that includes kissing, hugging, petting, free-sex-ing, and a lot of other -ing out there. Lol.
Look, I am as innocence as I am acclaiming. I have no reason to lie to anyone. So just believe what you want to believe. Not my problem. =)