mayhap

Chrétien would be so chagrinned. Himself profoundly antipathetic towards adulterous love, he introduced the world to the most popular adulterous couple of all time, surpassing even his unfavorite, the Tristan/Iseut juggernaut, which he alternately bashed and deconstructed in Cligés.

To be fair, I wouldn't say his handling of the Lancelot/Guinevere romance was exactly wholly responsible for the subsequent popularity of the pairing. Although he includes a perfunctory love scene where a bloody-fingered Lancelot bends metal bars to hook up with an imprisoned Guinevere while Kay, gravely wounded by his usual combination of bravado and poor planning, sleeps unwittingly in the same room, there isn't much of a payoff to their relationship. They don't get a happy or a tragic ending together—in fact, in the final penned by Godefroy de Leigny after Chrétien, having stranded Lancelot in a tower, pawned the thing off on him with some kind of outline to work from, at least one scholar apparently thinks Lancelot is more into the evil Meleagant's little sister, who rescues him from said tower, although I think he's reading way too much into a little hugging and kissing, which is pretty vanilla for Lancelot, whose relationship with Guinevere has strong D/s overtones.

When the two of them see each other again at Arthur's court, Guinevere "came somewhat to her senses / and put the matter to one side, / until the time she'd seen and spied / a good and private place at court, / where they would have a safer port / than at the moment was their lot." (No word on Lancelot's feelings about the matter, however.) Lancelot finally kills Meleagent, and that's the end. All the interesting stuff happens in later versions.