Symbolism, Imagery, Allegory
Sometimes it just seems like the person you're into could ask for anything, and you'd give it. You feel almost like a vassal or servant to someone who has power over you because you're just so in love. Sounds a little rough, huh? Tristan and Yseut can tell you all about it.
Longing for the sight of Yseut, Tristan asks love to grant him his desire to hold her in his arms once again, personifying love as a deity or lord that can grant "boons"—special requests from her vassals (18.152). Later, he tells Brangain that he is seeking a reward from Yseut "for only a quarter of my service to her, or for a half of my suffering" (18.157), making himself into a loyal servant of his mistress, Yseut.
Tristan also complains that his mistress (love) has failed to reward him for his service as a good mistress ought to. These ways of personifying love and characterizing the beloved use categories from the feudal economy. Which is what you'd expect, really, since that was what Béroul knew about when he was writing this. The reward for loving—returned love, and sex, too!—becomes nothing more than what love or the beloved owes her faithful vassal.