"The god of love, a benedicite!
How myghty and how greet a lord is he!
Ayeyns his myght ther gayneth none obstacles.
He may be cleped a god for his myracles."
(Knight's Tale, I.1795-88)
C. S. Lewis famously defined courtly love as "Humility, Courtesy, Adultery, and the Religion of Love." [C.S. Lewis, The Allegory of Love: A Study in Medieval Tradition. London, 1936 (rpt. 1958) [PN688.L4 1958x]. [Widener Lit 596.8.20]. (Charming, but use with caution; some ideas are a bit dated).
This fits well with courtly love as it was defined by Andreas Capellanus in the twelfth century. On the manners appropriate to a courtly lover in the fourteenth century, see Romaunt vv. 2175-2716, pp. 710-715, in the Riverside Chaucer. Note that in the Romaunt adultery is not in question, and the anti-social trait of Jealousy (which Andreas thought essential to love) is barred from the Garden of Love (See Romaunt, Fragment A, in the Riverside Chaucer). For a rather charming treatment of intended (but thwarted) adultery, with the lover finally rewarded for his devotion (fifteen children), see the brief romance The Earl of Toulouse. On the whole question see "Courtly Love and Chivalry in the Later Middle Ages."
The Knight of Latour Landry describes his love for his deceased wife in the prologue to his book of instruction for his daughters. He is something of a prude, and he is shocked at the flirtatious talk of a young lady.
The religion of love is apparent in the language of lovers (see Chaucer's "Complaint to His Lady," pp. 642-43 in Riverside Chaucer) and in the lightly humorous "The Lover's Mass."
For a set of rules of love for women (15th cent.) see: The Ten Commandments of Love.
For a defense of women and an illustration of how closely intertwined are courtly love and anti-female satire and thought, see Christine de Pisan's Epistle of Cupid, adapted into Middle English by Thomas Hoccleve.
For a number of examples of Middle English poems employing the conventions of courtly love, see:
The main difference between courtly love as Andreas defined it and courtly love as Chaucer knew it was the idea that love ennobled the lover -- made him a better knight. This is one of the topics debated by the Knight of La Tour Landry and his wife -- he arguing that his daughters should observe some of the conventions of courtly love, she stoutly maintaining that they should pay little attention to what clever men might say about such matters.
Medieval ideas of secular love were greatly influenced by Ovid; see his Ars Amatoria, tr. J. H. Mozely, Loeb, Cambridge, 1947 [Widener Lo 10.201.23] and his Remedia Amoris [P A6522.A8 G7 1977]. These works are available on line, translated by A.S. Kline on the Great Books and Classics site. The idea of the ennobling power of love owes something to Cicero's De amicitia, On Friendship Or see the Loeb edition, tr. William A. Falconer, 1923 [PA 296.C2 1923x]
Love was could also be a sickness -- the "loveris maladye of Heroes" (KnT 1373-74). See: Mary Frances Wack, The Liber de heros morbo of Johannes Afflacius and Its Implications for Medieval Love Conventions, Speculum, Vol. 62, No. 2. (Apr., 1987), pp. 324-344 (available in Jstor).
For further reading see the brief bibliography in the Riverside Chaucer, p. 777; to this may be added (for those interested in the early history of courtly love): C. Stephen Jaeger, The Origins of Courtliness: Civilizing Trends and the Formation of Courtly Ideals, 939-1210. Philadelphia, 1985 (GT350.J34 1985).