This holiday is observed around the world but a closer look will reveal that it is, in fact, a very unholy day. The word holiday comes from the combination of the words "holy" and "day" and originally was used to describe religious observances.
This holiday was originally called St. Valentine's Day and was established by Pope Gelasius I in the year 496 A.D. This pope is known most for how he pushed the philosophy of papal authority over all believers. He asserted that the pope was supreme due to direct succession as the Bishop of Rome through the Apostle Peter. He abolished the Roman pagan festival of Lupercalia which was associated with fertility and purification.
The holiday was originally established to celebrate the love that was demonstrated by various saints to their fellow man. This love was demonstrated by their provision for the poor as well as other acts of putting others before oneself. Slowly, it was changed to just a demonstration of love for the spouse that God had given a person or to that other special person in your life.
What started as a day of religious observance (holiday) became just a celebration of love. The biblical definition of love (see 1 John 3:16), as demonstrated by Jesus Christ and several saints with the name Valentine was even replaced. Now, this unholy day has become simply a celebration of sexual relations. Love is an act of sacrifice (putting others ahead of yourself) and not some cheap relationship that is bought with candy, flowers, diamonds, or anything else.
Over the years this festival for the saints was influenced more and more by pagan customs. This unholiness eventually led to Pope Paul VI removing it from the Catholic calendar in 1969. (look at the calendar on your wall and compare St Patricks Day with Valentines Day and you will notice that the St. is missing)