The scripts for Game of Thrones season 8 have clarified Jaime Lannister's reasoning for leaving behind Brienne in Winterfell while he ran back to his sister, Cersei. Brienne's reaction to Jaime's decision was clouded in controversy considering her previous character development. The original script would have shed more light on Jaime's actions in "The Last of the Starks."
Brienne of Tarth (Gwendoline Christie) was never taken seriously as a woman warrior in Westeros. She was often met with mockery despite proving herself over and over again. Brienne was an admirable fighter and a fierce protector, qualities that Jaime (Nikolaj Coster-Waldau) instantly recognized in her, becoming one of her closest friends throughout Game of Thrones. Prior to the Battle of Winterfell, Brienne revealed that she was never knighted despite her position among royalty. Jaime then made Brienne a knight and the pair fought side by side during the tumultuous battle.
Following the defeat of the Night King and the Army of the Dead, Brienne celebrated with those who she called friends, including Jaime. During the celebratory talk, Brienne was outed as a virgin before she slipped away to her room. Jaime followed and the pair finally gave in to their attraction, sleeping together. After the pair had sex, Jaime remained awake before he decided that he needed to return to King's Landing to support his sister through Daenerys' incoming attack. Brienne begged her new lover to stay but he claimed that he wasn't a good man life she wanted to believe. According to the Game of Thrones scripts available at the Writers Guild Foundation Shavelson-Webb Library in Los Angeles (via Insider), Jaime felt like a "traitor" after his romantic night with Brienne, leading him to the decision that he needed to go back to Cersei.
The Game Of Thrones Script Changes Made The Jaime/Brienne Situation Worse
After Brienne was knighted and made into a hero during the Battle of Winterfell, fans weren't too pleased with how she was made into a blubbering fool running after a man. This went against everything that the character stood for throughout the Game of Thrones. There was no question that Jaime had some sort of feelings toward Brienne but the way the relationship played out caused a lot of backlash from viewers. The scenario made it seem like Jaime won Brienne over and then tossed her aside to get back to his true lover/sister. Had the episode followed the original script, the series would have had a chance to justify Jaime's decision.
Following their love scene in the Game of Thrones script, "Brienne sleeps the sleep of the happily drunk and devirginized" while Jaime remained awake because he thought about how he helped save the world but couldn't let go of the fact that he still felt like a traitor. This feeling of guilt stemmed from how he left Cersei behind to join Winterfell's mission. That emotion was not necessarily exhibited on-screen. If anything, the episode made it look like Jaime jumped at the chance with Brienne but knew full well that he would go back to Cersei. He didn't leave Brienne in Winterfell because he worried about being a bad guy in the eyes of his new allies. Jaime left because he couldn't live with himself knowing that Cersei could potentially die alone. After his fling with Brienne, Jaime fully realized that his loyalties remained with Cersei and there was no way to change that considering his overwhelming feeling as a traitor.