As I was trying to figure out what to write next, I went back to poking around medieval ballads. I came across The Lays of Marie de France. I downloaded the book at Project Gutenberg and read it.
Unlike other collections of this sort, the works in Lays are mainly romantic stories. One or two have themes of friendship and platonic love, but most are about romantic love between men and women. There are tales of the triumph of love, interrupted love, and the betrayal of love. I recall at least one being about adultery.
Perhaps the most well-known of the stories in the Lays is "The Bisclavret." It's an early werewolf story. Strangely, it's not about how the man turns into a werewolf, or how a woman falls in love with a man who's a werewolf. It's about loyalty, both to partner and to the nobles you have to answer to.
Originally these works were written as ballads to be sung orally. However, the most common way to get the stories today is to read them as text. While there is something to be said about losing the poetry of a ballad, these works were written in French (albeit for an English king). Any translation out of the original language wouldn't be ideal for getting the flow of the ballads. As it is, these stories seem to be told in full as text, which makes for good reading.
Overall I enjoyed the Lays. A couple gave me ideas for stories I'm writing or planning to write. If what I've described interests you, go ahead and download the collection (seeing as it's free.)