Bennett's sexual allegory
The affair between Isadora and Adrian has an archetypal structure. It is a cuckolding story, but that isn't obvious until Bennett discovers his wife sleeping with a superior man. This particular version of the fetish is one where Bennett seems to have a passive curiosity about homosexuality (a curiosity probably linked to a real past experience), and where Bennett seems to need for his wife to cheat in order to be close enough to actually experiment. When Bennett becomes aroused and starts joining his cheating wife and her new boyfriend, the allegory is complete. The psychoanalytic value here is that Bennett deals with chronic feelings of inferiority and a passive interest in men, probably from past trauma.
Brian's sexual allegory
The question of genius is raised by the book. There is an implicit danger for damaged people with extraordinary intelligence, a problem that quickly spirals into something very serious. Brian is an undeniable genius, but as he grows older and continues learning and growing, the tantric relationship he has with himself gets blown out of proportion, and he begins to become schizoaffective, often believing he is Jesus Christ reincarnated (a somewhat Buddhist opinion), but then, he becomes violent and rapes his wife and beats her. His "religious enlightenment" is completely isolated, and he doesn't care about the outside world. He only cares about the beauty of his genius.
The motif of sexual fantasy
Every character in this story has dabbled here and there with sexual misbehavior (not to imply moralism; they do literally feel they are misbehaving). Since they are all psychoanalysts, they share many opinions about this fact, but basically, what they agree on is what sexual fantasy represents: it is the mind imagining solutions for traumatic memories and chronic existential pains, so when the characters behave in sexually gratuitous ways, that is what is being represented—a deep longing for peace and health.
The journey through Europe
Speaking of fantasy and reality, Isadora's story is an allegory about taking fate into her own hands and making her fantasy into a reality. She decides that she will not be controlled by shame or fear, and when she detects sexual chemistry between herself and Adrian, she goes the tantric path. Their affair is passionate, and although it seems that her husband will hate her for it, it turns out that his sexual desires were to be cuckolded. They are compatible.
The journey represents Isadora's sexual liberation with her dream guy on a dream trip through Europe, filled with sex and deep intimate conversations. At the end of the experience, though, she returns to her real life, leaving the reader puzzled, scratching their head.
Basically, this can be understood as an allegory for freedom, that only shame and stigma keep us from being happy. When she returns, she shows the other side of the coin, that family and honor have their place—she returns to her husband.
The stranger on the train
Although the novel seems to be a boisterous depiction of freedom in sexuality, there is an important thing to be noticed. Isadora has a fantasy about rape, and this novel treats that fantasy differently than any other fantasy. Isadora finds herself being seriously molested by a stranger on a train, and she is not aroused by it at all. She is terrified and horrified, but the fantasies had convinced her that if it happened, that she would love it.
When she reflects on this, she discovers that, yes her life events did seem to perfectly correspond to her fetishes, but that the reality of the experiences should be considered more seriously, more deeply. In a word, she feels that she became delusional in her sexual efforts.
