It's a 14th century poem set to music. The text is a virelai by Guillaume de Machaut (I think), but the composer of the music is anonymous. I think that it could be a dance, and it is a troubadour song (maybe trouvere, I'd have to check), so I don't believe it would have been used in a play.
Edit: I found a recording of it. (It stops early)
http://cdbaby.com/cd/istanpitta (track 10)
Keep in mind that this group has taken a lot of liberties with the score, but that's expected. The only thing actually written down is the vocal line.
Edit x 2: Hmm. They're not modulating the key. When I was fooling around with the tune, I was switching keys, but their lute player is just staying on D the whole time. And the vocal line isn't being doubled by instruments, which is something I was expecting for us to do. Options, options!
Edit x 3: Here's an early attempt at playing it. I need to practice.
http://www.soundclick.com/bands/songInfo.cfm?bandID=658240&songID=4954895It sounds a lot better with reverb, but I'm not trying to make a good recording of it. Just something I can show to the rest of the group before we get together again.