All through Book I, all I could think of was The Waste Land, specifically the Fire Sermon with its sterile, dutiful sex and dispassionate interactions.  While Brett and Jake clearly care deeply about one another, they react to their feelings with frustration and annoyance rather than with the wonder and passion one would normally expect of their age and situation.  They tell everyone that they have their careers to think about, but this irritating thing called love keeps getting in the way, mucking things up, throwing them in with one another against their better interests. 

It took more than one readthrough for me to catch on to the actual issue, which brought to mind more of The Waste Land, n the form of the Fisher King.  Career, duty, and practicality seem to be the priority for both characters, especially Brett, who is about to enter her third loveless marriage, which is what I assumed to be the issue.  While these may play a minor role, though, the largest issue is that of fertility.  From what I could pick up, she seems to be entering these marriages because, while she loves Jake, he cannot give her what she needs.  It is quite clear from the momentary lapses, when she is drunk, open, and upset, that Jake is the one she wants to go to, but the "wound" that he refers to more than once seems to be of a sexual nature, analogous to the Fisher King's wound.  Perhaps out of dutiful commitment to reproduction, perhaps out of a desire for sex, Brett chooses the whole men over the broken one she loves.

The worst thing about the whole situation is that it has clearly broken these characters.  Jake drifts, watching his friends gain women, lose women, abandon women, in almost a mockery of his own inability to do any of these things.  He cannot fathom Cohn's inability to fight back when being berated by Frances, because if he had what Cohn had, he'd defend it.  Brett, on the other hand, has found love bitter and unfulfilling, and as a result, plunges herself into marriages with men she does not love, sex just for the sake of itself rather than for herself or for another person, party after party with man after man falling hard after her.  If the love she holds dear can be so cruelly held against her, why not do the same to others?  In this light, the "booty call" of the Fire Sermon makes infinitely more sense than it ever has before.