Valentine was a Roman Priest at a time when there was an emperor named Claudius who persecuted the church. He had an edict that prohibited the marriage of young people. This was based on the hypothesis that unmarried soldiers fought better than married soldiers because married soldiers might be afraid of what might happen to them or their wives or families if they died.
Valentine lived in a very permissive society. Polygamy would have been much more popular than monogamy. And yet some young couples seemed to be attracted to Christianity. But obviously the church thought that marriage was very sacred between one man and one woman for their life and that it was to be encouraged. And so it immediately presented the problem of what the church should do about this.
The idea of encouraging them to marry within the church was what Valentine was all about. And he secretly married them because of the edict.
Valentine was eventually caught, imprisoned and tortured for performing marriage ceremonies against the command of Emperor Claudius the second. There are legends surrounding Valentine's actions while in prison.
One of the men who was to judge him in line with the Roman law was a man called Asterius, whose daughter was blind. He was supposed to have prayed with and healed the young girl with such astonishing effect that Asterius himself became a Christian.
In the year 269 AD, Valentine was sentenced to a three part execution of a beating, stoning, and finally decapitation all because of his stand for Christian marriage. The story goes that the last words he wrote were in a note to Asterius' daughter. He inspired today's romantic missives by signing it, "from your Valentine."
Beloved, let us love one another, for love is from God, and whoever loves has been born of God and knows God. Anyone who does not love does not know God, because God is love. In this the love of God was made manifest among us, that God sent his only Son into the world, so that we might live through him. In this is love, not that we have loved God but that he loved us and sent his Son to be the propitiation for our sins. Beloved, if God so loved us, we also ought to love one another. 1 John 4:7-11