What metaphors are used in The Glass Room by Simon Mawer?

In Part IV, the story of Ondine becomes a metaphor for Tomas' relationship with Zdenka and Eve. Zdenka, a beautiful ballerina, seems ethereal and otherworldly. Eve, on the other hand, seems to be very human. Zdenka's relationship with Tomas seems extremely idealistic yet serious, while his time with Eve is fun and light. Tomas can tell that if he plays with Zdenka's heart she will break. As of now, he is not sure whether or not she will be able to curse him the way that Ondine cursed her lover.