As with so many holidays, Valentine's Day (or at least the name) has Christian roots. There's some dispute over how many St. Valentines there were and which one has any connection with the current observance. According to Catholic Online, credit is generally given to a priest named Valentine who helped Christian martyrs in Rome persecuted under Claudius II. Aiding martyrs was a crime, and Roman authorities apprehended Valentine. According to text found next to a woodcut of St. Valentine in The Nuremberg Chronicle, published in 1493 (and not available through Amazon), he was also caught marrying Christian couples. There are two accounts of what led up to his eventual execution on February 14. One is that he refused to renounce his faith. The other is that he tried to convert the emperor. Either way, he was beaten, stoned, and finally beheaded. One legend has it that on the eve of his execution, he signed a farewell note to his jailer's daughter, "From your Valentine."
In A.D. 496, February 14 was set aside by the church to honor his martyrdom.
Modern customs associating Valentine's Day with romantic love are believed to have their roots in the France and England of the Middle Ages. At that time, it was generally believed that halfway through the month of February, i.e., February 14, the birds began to pair. Hence this reference in Chaucer's "Parliament of Foules":
For this was sent on Seynt Valentyne's day
Whan every foul cometh ther to choose his mate.
The day became known as an occasion to write love letters and send tokens of affection, and was named for the saint's day upon which it fell.
Although it's a secular holiday, perhaps Christians would do well to remember St. Valentine and the sacrifice he willingly made out of a different kind of true love.