Short answers, pulled from the story.
The 8th-century Gelasian Sacramentary recorded the celebration of the Feast of Saint Valentine on February 14. This early Christian document honored a martyr named Valentine though historical records from that era remain sparse and often contradictory.
Valentine of Rome was martyred in 269 while Valentine of Terni died during the persecution under Emperor Aurelian in 273. Both men are primarily associated with this date but their relics rest in different locations including the Via Flaminia and churches in Rome and Dublin.
The day became associated with romantic love in the 14th and 15th centuries when notions of courtly love flourished. Geoffrey Chaucer wrote the Parliament of Fowls in 1382 as a dream vision portraying birds choosing mates on Saint Valentine's Day to establish this connection.
Paper Valentines became so popular in England in the early 19th century that they were assembled in factories after postal reforms reduced rates following Sir Rowland Hill's invention of the postage stamp known as Penny Black in 1840. The U.S. Greeting Card Association estimates that approximately 190 million valentines are sent each year in the US which rises to 1 billion when school activities are included.
In Brazil the Lovers' Day is celebrated on June 12 because February 14 falls too close to Brazilian Carnival while Colombia celebrates Love and Friendship Day on the third Saturday in September instead. Japan introduced the holiday for the first time in 1936 but later developed unique customs like White Day on March 14 where men return gifts given by women.