It is St. Valentine's Day. Here is some of the history of Valentine's day that I know. I don't know the entire story. I do know that most of our 'Christian' holidays were set up to counter the pagan holidays of various reasons. read more
The day was named after St. Valentine. So when people say Valentine's, they are referring to the saint's day. To say Valentine, is still referring to the saint, but more personal to you. In other words, you are leaving out the saint's day and making it yours. Both are alright. I hope that makes sense. read more
While some believe that Valentine’s Day is celebrated in the middle of February to commemorate the anniversary of Valentine’s death or burial (a martyred Christian saint)–which probably occurred around A.D. 270–others claim that the Christian church may have decided to place St. Valentine’s feast day in the middle of February in an effort to “Christianize” the pagan celebration of Lupercalia. read more
The ngram below graphs the use of Valentine’s Day and Valentines Day in a large number of English-language texts published between 1900 and 2000. The spelling without the apostrophe has gained a little ground but still hardly competes against the more common form. read more