Valentine's Day - as the holiday was named after a Christian priest - Valentine.

The Catholic Church recognizes at least TWO saints named Valentine, both of whom were martyred.

One Valentine lived in Rome in the 3rd century and was a priest. In those days, Emperor Julius Claudius II ruled, and decided that the soldiers in his army should be single guys, and not men with wives and children. He issued a decree prohibiting weddings for young men - future legionnaires.

History dates back to 269, when the Roman Empire was ruled by Emperor Claudius II. The warring Roman army experienced an acute shortage of soldiers for military campaigns, and the military leader was convinced that the main enemy of his military plans was marriage, for a married legionnaire thought much less about the glory of the empire than about how to feed his family. And in order to preserve the military spirit in his soldiers, the emperor issued a decree forbidding legionnaires to marry.
But Valentine, as a priest, understood the injustice of the prohibition and continued to secretly marry his beloved.

From the ban of Claudius II, the soldiers did not become less in love. And to their happiness, a man was found who, not fearing the imperial wrath, began to secretly marry the legionnaires with their beloved. It was a priest named Valentine from the Roman city of Terni (Valentine of Terni). Apparently, he was a real romantic, since his favorite pastimes were to reconcile those who quarreled, help write love letters and give flowers to their beloved at the request of the legionnaires, on their behalf.

As soon as Claudius II found out about this, he decided to stop the "criminal activity" of the priest, and the priest was sent to prison.
The tragedy of the situation was also that Valentine himself was in love with the jailer's daughter. While in prison, Valentine fell in love with the overseer's blind daughter and with his love healed her from an illness. According to the legend, the jailer personally asked the priest to heal his daughter, and she fell in love with Valentine ...
And, for his benevolence and sinful love, he was sentenced to death, which took place on February 14.
The day before the execution, the priest wrote a farewell letter to the girl, where he spoke about his love, and signed it "Your Valentine".
The letter was read after he was executed.

Subsequently, as a Christian martyr who suffered for the faith, Valentine was canonized by the Catholic Church.
And in 496, Pope Gelasius I declared February 14 Valentine's Day.

Since 1969, as a result of the reform of the divine services, Saint Valentine was removed from the liturgical calendar of the Catholic Church (along with other Roman saints, information about whose life is contradictory and unreliable). However, even until 1969, the church did not approve and did not support the traditions of celebrating this day.

Another Valentine lived near Rome. He was famous for his healing abilities and ... food addictions. The people jokingly called him "a doctor - a deli", because Valentin always prepared only delicious medicines.
In addition to healing bodily anguish, he knew how to heal the soul from love longing with prayers. In pagan times, Valentine openly professed Christianity, for which he was executed. Above his grave, grateful parishioners built a basilica, above the entrance to which they hung the inscription: "Valentine, patron saint of Love."

Whether it was so or otherwise, but, most likely, it was from there that it was customary to write love notes on Valentine's Day - "Valentines".
They also like to arrange weddings and get married on this holiday. It is believed that this will become a guarantee of eternal love.