So, they say that one of the 14 St Valentines was the first St. Valentine.
And then there is all sorts of stuff about the Romans and Lupercalia and mid-February.
Paper valentines began to be exchanged in the 5th century, with a real peak in popularity in the Victorian era.
Esther Howland is credited with the commercial American valentine industry, and the Greeting Card industry now hands out a Esther Howland Award for greeting card visionaries.
Personally, I have never really understood the allure of Valentine's day-- aside from the spike in the availability of cinnamon candy