History of Valentine's Day:

Valentine's Day, also called Saint Valentine's Day or the Feast of Saint Valentine

is an annual holiday celebrated on February 14.

It originated as a Western Christian liturgical feast day honoring one or more early saints named Valentinus, and is recognized as a significant cultural and commercial celebration in many regions around the world, although it is not a public holiday in any country.

Saint Valentine  was imprisoned for performing weddings for soldiers who were forbidden to marry and for ministering to Christians, who were persecuted under the Roman Empire. According to legend, during his imprisonment, Saint Valentine healed the daughter of his jailer, Asterius, and before his execution, he wrote her a letter signed

"Your Valentine" as a farewell.

The day first became associated with romantic love within the circle of Geoffrey Chaucer in the 14th century, when the tradition of courtly love flourished. In 18th-century England, it evolved into an occasion in which lovers expressed their love for each other by presenting flowers, offering confectionery, and sending greeting cards (known as "valentines"). In Europe, Saint Valentine's Keys are given to lovers "as a romantic symbol and an invitation to unlock the giver’s heart"

References:

en.wikipedia.org/wiki/Valentine's_Day