Yes, it is also the feast of St. Valentine, though I can find no connection between the third century martyr and our current amorous practices. Valentine was a Christian who didn't survive a beatdown on the Milvan Bridge. It happened a lot. So often that nothing much more was said about it.
Then a thousand years later, the great fourteenth century ornithologist Geoffrey Chaucer observed that birds select their mates on the feast of St. Valentine. The Romans had known this as a courtship day centuries prior to Valentine's demise, which is why they held their feast of Lupercalia on or about mid-February. So the American Candy Council got together with the Greeting Card Publishers Association to bring us... a Happy Valentine's Day.
Of course, both the Eastern and Western calendars agree that it is the feast of St. Cyril. The East honors his brother on April 6, which is somewhat more respectful as they had divergent careers, but the West assigns a common day to acknowledge their shared ancestry and mission.
Cyril and Methodius were sent east to the Slavic countries to preach the Gospel. They invented a modified Greek alphabet (cyrillic) into which they could translate the Bible. They preached in the native Slavonic languages, to some distress of the Western missionaries working there. There was conflict, but each of the brothers was assigned a bishop's mitre. Cyril died before he received his, and Methodius was imprisoned by German missionaries on charges of heresy, but cleared and released. Apparently he ran afoul of them often, but was always cleared.
There is little doubt of their enormous contribution to the shape of our cultural landscape, having been so successful in bringing Russia and its fellow Slavic countries into the Eastern Orthodox faith. Our understanding of Europe itself is imprinted with their work. This seems far more worthy of acknowledgment that bleeding out on the Milvan Bridge (with all due respect to the Roman martyrs who did so).