One of the many themes of Game of Thrones has always been a story about how childhood experiences warp characters into the people they become. The most obvious of these has always been Sansa, which is perhaps why she is so controversial. However, it holds for Daenerys as well, whose experiences with the Dothraki and in Meereen have shaped her. It's also true of the older characters as well, like Cersei and Jaime, and may be why they are on a crash course. But will Jaime kill Cersei in Game Of Thrones Season 8 Episode 5? His decision to go back may be his undoing.
Jaime is someone who begins the series as an antagonist. He's cocky, a golden knight bully who thinks of nothing but glory. Then, in a twist of twists, fans discover he's sleeping with his twin sister, and willing to kill a child to keep it secret.
It seems a bizarre and horrid set of life choices, but over the seasons, Jaime's upbringing and his intensely misguided sense of family loyalty explain how viewers found him in such a position at the end of the Season 1 pilot. Tywin's iron fist upbringing and the overarching lesson that anyone who wasn't a Lannister was the enemy, mixed with Jaime's emotional bond with Cersei as a twin, and the miserable household after Joanna Lannister's death created a toxic stew. In it, the two turned inwards to each other, as the only ones they could trust.
Throughout the events of Game of Thrones, Jaime has slowly realized just how toxic his relationship with Cersei is. It took seven seasons for him to stand up for himself, to say "I deserve better," and to leave. However, Tyrion is right when Jaime claims that he finally saw through their sister after all those years. Jaime always knew what she was, and he loved her anyway. He just believed himself to be an equally garbage person who didn't deserve anything better and behaved accordingly.
The tragedy of Jaime's final season is that he tried to reach for something better with both hands. He decided to leave that garbage person behind. He committed himself to Brienne, trying to substitute one relationship for another. But, as most addicts who have attempted to go sober and wound up as dry drunks, replacing one addiction for another, that's not the path to success. The moment Jaime heard the news about Cersei taking down one of Daenerys dragons, he snapped back. His sister had signed her own death warrant. Jaime had to get there to save her.
It's the worst choice he could have made. Going back to being a garbage person to die at the side of his sister is an irrational, emotional response. How badly will Jaime react, especially when he arrives to see her bedding Euron instead? How terrible will their reunion be, with Cersei sneering at Jaime for being a weak traitor to her and their house?
Will Daenerys get to take down Cersei? Or will Jaime snap once and for all, and, per the Valonqar prophecy, strangle her in a crime of passion before the Mother of Dragons even gets the chance?