Take your pick, St Valentine was either martyred for disobeying an edict by Claudius II prohibiting marriages and engagements, or else he restored the sight of a Judge’s daughter and the Judge converted to Christianity.
There might be some credibility to a military leader prohibiting marriage. The myth suggests that monogamous relationships would weaken the Roman army with soldiers fearing for their lives in battle and worrying about their unprotected wives and children. Married men may have been excused military service. So if Valentine was conducting marriages in secret and Claudius found out, he would have been a bit miffed
In any event, martyrdom for Valentine was accompanied by great brutality. Valentine was tortured, beaten to death and hanged, which seems excessive.
My own contribution to the forthcoming love fest appears on the odd ode or two page on this blog – Dancing in the Waves.