The story, which first turned up in twelfth century Celtic folklore from northern France, has subsequently inspired Sir Thomas Malory, a Wagner opera, and several films. This painting of the legendary lovers is by the British Victorian painter Herbert James Draper (1864-1920).
Although Sabina uses Tristan to symbolize the “romantic lover” part of Tomas that is in opposition to his libertine half, the situation is a little more complicated than that, because Iseult keeps her pledge to marry King Mark, after which the lovers continue their affair, which is technically adulterous.
There is a second likening of Tomas to Tristan in the novel (again, in Sabina’s mind), in section 10 of Part Three (page 124 in this edition), when Sabina is in Paris some years later and receives the news that Tomas and Tereza have died together. He died as Tristan (the romantically faithful), she thinks to herself, not as the adventurous Don Juan.