I studied news writing while in college. I was told of "the five W's and the H" of a news story. We were taught to answer these six questions in the first paragraph and expand on them in the rest of the story. Below are the five W's and the H of our Valentine's Day, February 14th.
St. Valentine of Rome, martyred AD 496 because he aided persecuted Christians. St. Valentine of Terni, Bishop, AD 197, also martyred-tried to convert Emperor Claudius II, who then ordered him executed. While in jail he Prayed for and healed the jailer's blind daughter who then became a Christian; resulting in the jailer's conversion, as well that of 44 of his family.
Several other St. Valentine's in legend. Their lives have been celebrated on June 6th and June 30th, as well as February 14th.
The first mentioned mention of romantic love association with Valentine's Day I found was in 1382. Geoffrey Chaucer wrote: "For this was on St. Valentine's Day, when every bird cometh there to choose his mate." This was concerning the young King Richard II's (of England) engagement to Anne of Bohemia in 1381, they were married in 1382, each 15 years old. Chaucer was referring to May 3, Valentine's Day of that year.
England seems to be where Valentine's Day was first celebrated as a day of romantic love. At first Valentine's Day was celebrated on May 3, 1381; then many years later on February 14.
As early as AD 300 there was a connection with healing of sickness, comforting the needy, etc. but romantic love was not connected to this day until the 1300's.
First a special day for the church, then later became a special day to tell of one's love for another. The first known Valentine Cards became in use, handmade, in 15th century. 1791 a book of verse to be used by lovers in hand written valentines. The next century postal rates came down and mailed printed valentines came into being.