According to church tradition, St. Valentine was a priest near Rome in about the year 270 AD. At the time the Roman Emperor Claudius II issued an edict forbidding marriage. When Claudius II became the emperor, he thought that he can make good soldiers. So, to assure good soldiers, he banned marriage.
St. Valentine saw the trauma of young lovers, so he met them in a secret place and joined them in the sacrament of matrimony. Claudius learned this and arrested Valentine and executed him on February 24, 270.