I hold resolve Valentine Day was arrived at based in reproductive science. The ultimate of love is marriage to bear offspring. The time when the ovum is released [ovulation] varies depending on the individual’s menstrual cycle, but it’s usually 14 days before the next periods start meaning there will no hindrance or limitation if couples decides to go overboard on this particular Valentine Day. What more, in ovulation phase female is in hormone driven attraction to male.
Why then the month of February? I assume tabulation based in measures of average. Most menstrual cycles are found to be within range of 21, 28 and 32 days. Since then we have no months of 21 and 32 days, but we have February of 28 save for limp year where February days are 29 days. February became automatic choice.