❝In the books, they are committing incest in a church next to the corpse of their dead son. […] In the books, Jaime is still not back from King’s Landing when Joffrey dies. He’s not there for the wedding. There’s a lot of speculation that he may be dead. He’s escaped; he hasn’t been seen. Various reports are reaching the capital, and Varys isn’t able to find him. All this is in there and then you have Cersei, who’s not a viewpoint character at that point in the books, so you really don’t know what she’s thinking. In my mind, she’s clearly thinking that Jaime may be dead. The only person she ever truly loved besides her children may be lost to her forever and suddenly there he is before her—but shockingly maimed and transformed. There is a mutual passion for each other. And it’s like if you get a cable that your husband has been killed in war, and then suddenly there he is—he’s not killed in war. That triggers something.❞
GRRM, for The Daily Beast
The only person she ever truly loved besides her children
GRRM says Cersei loves Jaime.
So to recap, Jaime and Cersei are for all accounts and purposes, husband and wife, he’s the only person she’s ever loved besides her children, and in the book, alter sex was consensual.
Today is a good day.