Why do we celebrate Valentine's Day?

"We celebrate Valentine's Day, because until 1969, it was one of the many Saint's Days observed by the Catholic Church. It was dedicated to the patron saint of romantic causes, St. Valentine.
Although it was removed from the Church's calendar in 1969, the religious meaning coupled with Valentine's Day's roots in Roman paganism have allowed it to continue as a holiday for everyone.
Early Christians saw Valentine's Day as a way to honor St. Valentine, of whom there were actually three. The Catholic Church recognizes three saints by that name, all who were martyred on February 14.
The St. Valentine the day is named for was, most likely, a priest in the 3rd century who performed secret marriages when the Roman Emperor Claudius II thought single soldiers were more likely to enlist in the army. That St. Valentine was imprisoned and executed on February 4, 270. It is believed he sent the jailer's daughter a note saying, "From your Valentine." The phrase is still widely used on valentines today.
In 496 A.D., February 14, was declared in the name of St. Valentine by Pope Gelasius. It remained a Church holiday until 1969, when Pope Paul VI took it from the calendar.
On February 14, the ancient Romans celebrated the Feast of Lupercalia in honor of Juno, the queen of the Roman gods and goddesses. Juno was also the goddess of women and marriage so honoring her was thought to be a fertility rite.
At the feast held the next day, the women would write love letters and stick them in a large urn. The men would pick a letter from the urn and for the next year, pursue the woman who wrote the chosen letter. This custom lasted until the 1700's when people decided their beloveds should be chosen by sight, not luck."