Below is from Wikipedia
Valentine's Day, also known as Saint Valentine's Day or the Feast of Saint Valentine, is a celebration observed on February 14 each year. It is celebrated in many countries around the world, although it is not a public holiday in most of them.
St. Valentine's Day began as a liturgical celebration of one or more early Christian saints named Valentinus. Several martyrdom stories were invented for the various Valentines that belonged to February 14, and added to later martyrologies. A popular hagiographical account of Saint Valentine of Rome states that he 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, he healed the daughter of his jailer, Asterius. An embellishment to this story states that before his execution he wrote her a letter signed "Your Valentine" as a farewell.
Saint Valentine's Day is an official feast day in the Anglican Communion, as well as in the Lutheran Church. Some part, but not all of the Eastern Orthodox Church also celebrates Saint Valentine's Day, albeit on July 6 and July 30, the former date in honor of the Roman presbyter Saint Valentine, and the latter date in honor of Hieromartyr Valentine, the Bishop of Interamna (modern Terni). In Greek Orthodox Church and other Churches of the Ecumenical Patriarchate, no Saint Valentine exists, nor venerated.
I made the above graphic.