It is of pagan origins, yes. The name comes from a man who was supposedly imprisoned and martyred for his faith - and he died on February 14th. He supposedly wrote letters to the warden's daughter, signed "love, Valentine." This date is typical of many Catholic feasts - associated with the time of someone's death, not their life.

The association with love (but actually sex) comes in at this time of year because it was the time when the Roman orgies went on (sorry, but there was no other way to say that delicately). That is why you will see many fertility symbols associated with this day. It was the mating time for the birds, cupid was the god of lust or sex.

There is nothing wrong with wanting to acknowledge or celebrate your love for your spouse, etc. - but I believe Christians should avoid the appearance of evil, and do so at a time not dictated by the lost world, and not associated with paganism and moral corruption.