courtly love

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An idealized and often illicit form of love celebrated in the literature of the Middle Ages and the Renaissance in which a knight or courtier devotes himself to a noblewoman who is usually married and feigns indifference to preserve her reputation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A mediaeval European conception of noble and chivalrous love, generally secret and between members of the nobility.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (Middle Ages) a highly conventionalized code of conduct for lovers