"Similarly, Jaime is a figure of chivalric love in the books—despite his arrogance and ruthlessness, his devotion and sense of duty to Cersei, the only woman he has ever loved, is so fervent as to border on adoration. Admittedly, the show can’t rely on his point-of-view chapters, as the book does, to communicate that love. But given what we have seen Cersei Lannister capable of—her ex-husband is hardly the only man she’s had killed—is it even conceivable that she would stand for it? Jaime raping Cersei is a major anomaly for these two characters—even based purely on what we’ve seen in the show. It’s just not something that either character would do."
Rape of Thrones · For Our Consideration · The A.V. Club
I’m really enjoying this A.V. Club piece, but I have to disagree with this wholeheartedly. So many romantic ideas of chivalry are fundamentally rooted in misogynistic ideals of women as weak and needing protection. The idea of a good knight championing a virtuous woman depends on the woman being virtuous, and even in the books we see that the deterioration of Jaime and Cersei’s relationship comes as a result of Jaime’s progressive loss of belief in Cersei’s virtue (even as Cersei’s rejection of Jaime is because he’s no longer physically capable of fulfilling his prescribed role in that knight/lady narrative).
In “Breaker of Chains” we see Jaime rape Cersei after calling her “hateful,” and it feels explicitly punitive. She no longer represents the ideal woman to him, and he considers this to be a betrayal of the spirit of their relationship. Also wrapped up in this moment is the idea that Cersei is at her most disempowered point right now and Jaime is also feeling powerless—but he still has the power to rape her. To me, this doesn’t seem shocking or even particularly out of character.
As far as whether Cersei retaliates, that remains to be seen on the show.