An interesting excerpt from Sex in History by Gordon Rattray Taylor:

...we begin to see, not immorality as such, but a completely different system of sexual morality at odds with the Christian one [during medieval times]: a system in which women were free to take lovers, both before and after marriage, and in which men were free to seduce all women of lower rank, while they might hope to win the favours of women of higher rank if they were sufficiently valiant. Chrestien de Troyes explains:

"The usage and rules at that time were that if a knight found a damsel or wench alone he would, if he wished to preserve his good name, sooner think of cutting his throat than of offering her dishonour; if he forced her against her will he would have been scorned in every court. But, on the other hand, if the damsel were accompanied by another knight, and if it pleased him to give combat to that knight and win the lady by arms, then he might do his will with her just as he pleased, and no shame or blame whatsoever would be held to attach to him."

As Briffault comments, however, the first part of the rule does not seem to have been regarded so strictly as the poet suggests. Traill and Mann say, "To judge from contemporary poems and romances the first thought of every knight on finding a lady unprotected was to do her violence." Gawain, the pattern of knighthood and courtesy, raped Gran de Lis, in spite of her tears and screams, when she refused to sleep with him. The hero of Marie de France's Lai de Graelent does exactly the same to a lady he meets in a forest - but in this case she forgives him his ardour, for she recognizes that "he is courteous and well behaved, a good, generous and honourable knight".