Thanks crispy sausage rolls
And going a bit further, look at Jamie and Cersei.
Jamie was never going to kill her, ever. Yes he committed pretty unspeakable crimes at the behest of Cersei but in his head it was to protect his family - he pushed Bran because himself, his children and his lover/sister would be killed should anyone know. Anything else he did was as part of his oath as a Kingsguard. That is why he went North. He was always an honourable man, yes he was selfish but he always looked out for his family and those he loved. He also spent years being branded a king slayer when he wasn't, it was the last course of action. He saved the realm and no one knew. He was never going to kill Cersei when he thought there was another way out to keep the peace and his family, his child, safe. I also don't believe Jamie used Brienne. He respected her, he knighted her and for a brief moment he saw a life he could lead but ultimately his love for his family and child won.
Cersei was another victim of circumstance. The only man she wanted, apart from her brother, loved Lyanna Stark. The man she ended up married to also loved Lyanna. No wonder she hated the North. Everything else, her descent in to madness, was to protect her children. She lived her life by a prophecy which foretold the death of her children and she desperately tried to undo this at every turn. Her walk of shame was for Tommen. Killing Robert and Jon Arryn to protect her children and her secret. Siding with and sleeping with Euron was to save her baby. Even in those last moments, surrendering and then fleeing, it was for her child.