I am beginning to have a theory about different types of erotic novels which are meant to appeal to different tastes or moods of their readers. One type, of which this was one, privileges the sex scenes over other types of scenes, which may be given short shrift. To me, this type of book seems more easily broken apart into a series of scenes meant to be read one at a time, perhaps one each night. Forward motion is less important than dwelling in each scene as it happens. The reader can get to know the characters, and added familiarity with them adds to the enjoyment of each subsequent scene, but there's not plot-fueled rush to find out what happens.
The type more to my taste has a driving plot; it doesn't have to be a complex or elaborate plot, but I do prefer a problem the characters must solve, with the sex scenes advancing them towards that goal. In fact, I prefer that the sex be part of the problem and its solution.
I have to think more on this--it's still a vague shape in my mind.