He was in fact a pagan priest jailed for helping Christians in Rome.
He restored the sight of the jailer’s blind daughter but was only rewarded by being clubbed to death. People doing miracles from jails — what would happen if this sort of thing was left unchecked?
His executioners did however forget to check the date. It was common belief that the fourteenth day of February was the day birds chose their mates.
Having a Martyr expire on this day gave humans the chance to have a Saint for this day and go all lovey-dovey too and give gifts and cards.
Poor St VALENTINE never got the chance to mate at all — unless the jailer’s daughter knows something we don’t.