Charlie Demers, that said "Valentine’s Day is just a corporate, Hallmark holiday cooked up to celebrate an indescribably brave 3rd century priest who gave succour to a persecuted minority & was executed by the most powerful state in the world for resisting its war-making!"
Well, that got me curious! Valentine was anti-war? Sure thing. He was indeed a priest who ministered in Rome in the days when Christians were still persecuted for their faith. He was jailed several times for preaching Christ and trying to convert pagans. The first time he was jailed for this he was released after he restored sight the the daughter of the judge who has tried him, convincing the judge and his whole household to be baptized. It's totally sounds like a story out of the book of Acts.
But the real act of non-violent resistance to empire is when Claudius II was having difficulty recruiting men to the Roman army. Because their attachment to family and spouses prevented them from their duty he banned all engagements and marriage in Rome. Valentine continued to perform marriages in secret for Christian couples so that the men would not have to enlist. When Claudius discovered this Valentine was arrested again, clubbed to death and beheaded. And that is why February 14 is Valentine's Day. It's the date in 270 (although the year is debated) that Valentinus of Rome was beheaded.
It's thought that the reason that it became instituted as a celebration of romantic love is that, like so many Christian celebrations, it supplanted a pagan holiday. In this case it was the holiday of Lupercalia, a pagan festival of love.
You're welcome and Happy Valentine's Day.
*Info above mainly from Wikipedia, History.com and Catholic.org