The motif of adultery
Adultery is when a married person has an affair with someone, or when another person chooses a mate who is already accounted for. Robin tries to connect with anyone, so the motif begins to become a portrait of her willingness to color outside of the lines that society has constructed for her, and she meets other people who are similar in that way, for better and for worse.
Nora as a symbol
Nora symbolizes Robin's willingness to experiment of course, but she also represents a kind of experiment that is helpful to Robin, because she is learning a new way of perceiving herself and romance by being with Nora. In the end, the same vices end that relationship that end all of Robin's affairs.
Church and religion
The ultimate symbol of the novel is the dog asleep in church, a portrait of nature at rest. Robin is not at rest though, at all, because her experience of church is emotionally complicated. The contrast of religion with nature is symbolic, because there is something at the church that she seeks to inherit and perhaps something in the religion that she hopes to avoid. The symbol is clearly a reference to her feelings toward God and fate.
The woods as a symbol
In the woods, everything is seen through the eye of nature. In other words, when people are in a coffee shop or something, they are in "people" mode, minding manners and such. But in the woods, there is a symbolic reversal back to "animal" mode. They are alert and they don't have perfect knowledge about their surroundings. In fact, the promise of the woods is that they are surrounded by wildlife.
Europe as a symbol
Europe represents a kind of Edenic state of societal participation, both because the cultures mentioned by the book are ones with social propriety, but also because Europe is the setting in the first portion of the book, and Nora and Robin share a heavenly experience of Paris that quickly decays into something more difficult and ordinary than they hoped.
