Now on to some history...
St. Valentine's Day honors a saint who, according to legend, married young Christian couples secretly, in defiance of Roman law. The Nuremburg Chronicle (1493) is the first printed record of this story. The story further states that Valentinus (the Latin form of the name Valentine) aided Christians who were being persecuted by the state. He was arrested and befriended emperor Claudius II. Unfortunately he was sentenced to death after trying to convert Claudius to Christianity. He is considered a martyr.
In addition to love, lovers, engaged couples, and happy marriages, Valentine is also considered a patron saint of beekeepers, epilepsy, fainting, greetings, plague, travellers, and young people. Bet you didn't know that. I sure didn't.
The source for the above is a website called Catholic.org. The link is to St. Valentine's page if you would like to do further reading.