Valentine was a priest in Rome and he was a martyr. He was made a saint but he had nothing to do with anything to do with romance. The name became associated with romance because a poem was written in the Middle Ages by Geoffrey Chaucer and it became traditional to write poems and send flowers and sweets to your sweetheart. The poems and cards were called Valentines.
Apart from his name, nothing is known about St Valentine other than he was buried at Via Flaminia on February 14, AD269. There is a myth, with no historical value, that he wrote a card to the blind daughter of his jailer the night before he was executed and he wrote “from your Valentine.”
From the 19th century Valentine’s cards have become mass produced, printed cards unlike the original hand written poems. So I think that it would be better to send a hand written card than a cheap old card from Hallmarks!