How did Saint Valentine become a saint?

Valentine would have done what all priest do: minister to their congregation. Valentine became a patron saint of lovers when the Roman Emperor made it illegal for couples to get married. He needed men for his army and could not draft married men. Valentine continued to marry couples in secret. When the emperor found out, he had valentine thrown into prison. While in jail he became a close friend of the jailer's young daughter. Just before he was executed for his crime, he sent her a letter in which he told her to remain faithful to God. He signed it, "From your Valentine."

He is a saint because he died for doing what was correct. he was a martyr.