The history of Valentines Day shares roots with both Christian history and the Roman Empire.
There are three saints currently recognized by the Catholic church named Valentine or Valentinus, all were killed for their faith.
"According to one legend, Valentine actually sent the first 'valentine' greeting himself. While in prison, it is believed that Valentine fell in love with a young girl — who may have been his jailor's daughter — who visited him during his confinement. Before his death, it is alleged that he wrote her a letter, which he signed 'From your Valentine,' an expression that is still in use today. Although the truth behind the Valentine legends is murky, the stories certainly emphasize his appeal as a sympathetic, heroic, and, most importantly, romantic figure. It's no surprise that by the Middle Ages, Valentine was one of the most popular saints in England and France." (History.com)
For this reason perhaps he is considered the patron saint of couples and lovers.
The date of Valentines day is thought to be associated with the death of Valentine, but it could also be because when the church was converting pagans and trying to incorporate dates of their holidays with those of the church, February was the month celebrated in pagan culture as the fertility month, official start of spring, and when they performed their "spring cleaning" by sweeping their homes and sprinkling salt and wheat about them. (history.com)
Valentine greetings were popular back in history as far as the Middle Ages, but it is a more recent celebration in the U.S. from a commercial point of view. The first commercial greeting card in the U.S. was 1840, it was created and mass produced by Esther Howland.
It is the second largest card sending holiday in the U.S.
So I send you Valentines greetings today.