What is the relationship between Gerda and Ulrich in the novel, The Man Without Qualities II: The Like of It Now Happens?

Gerda and Ulrich are friends. Now and then, attraction comes up during their friendship, but only on one occasion does it get any "steamier" than normal. This leads to an extreme experience where Gerda ends up screaming; what it really is is that neither she nor Ulrich actually want to go through with having sex with one another although they enjoyed some smooching very much.