Courtly Love
In the middle ages, marriage often consisted of mere contracts. The idea of marrying for love, and not convenience or the sensibility of the match, was a foreign idea. However, the concept of courtly love suggests that one can love even while married. Courtly love is a set of guidelines based upon the chivalric ideals of the time period for which a knight, or nobleman, must adhere to when he is in love with a married woman of equal or higher rank. It is a form of sanctioned adultery. The affair between the knight Lancelot and the married Queen Guinevere exemplifies the characteristics of courtly love.

Characteristics of Courtly Love:
Other resources:
http://www.li.suu.edu/library/courses/HUM101/31rules.htm
http://www.encyclopedia.com/articles/03206.html
http://www.gloriana.nu/courtly.html
http://encarta.msn.com/index/conciseindex/10/010B2000.htm?z=1&pg=2&br=1
http://www.multimedia.calpoly.edu/libarts/dschwart/engl513/courtly/courtly.htm