For a fun history of how chocolate became a Valentine’s treat, see this article:

https://www.washingtonpost.com/news/retropolis/wp/2018/02/14/we-owe-our-sinful-valentines-day-chocolates-to-the-prudish-self-denying-cadburys/?hpid=hp_hp-more-top-stories-2_retro-valentinesday-746am%3Ahomepage%2Fstory&utm_term=.ccf5c5b84d4b 

And for a terrific history of the paper Valentines, see the New York Times: