I'm taking a music appreciation class at the moment, and my prof. played this in class (we just finished going over ars nova):



I absolutely love it. Here are the lyrics (in Old French and English)
Puis qu'en oubli sui de vous, dous amis.
Vie amoureuse et joie a Dieu commant.
Mar vi le jour que m'amour en vous mis.
Puis qu'en oubli sui de vous, dous amis.
Mais ce tenray que je vous ay promis.
C'est que ja mais n'aray nul autre amant.
Puis qu'en oubli sui de vous, dous amis.
Vie amoureuse et joie a Dieu commant.

Since I am forgotten by you, sweet friend,
I bid farewell to a life of love and joy.

Unlucky was the day I placed my love in you;
Since I am forgotten by you, sweet friend.

But what was promised you I will sustain:
That I shall never have any other love.
Since I am forgotten by you, sweet friend,
I bid farewell to a life of love and joy.