"Everything they do, they're following someone else's agenda all the time - by choice."
Jaime fights for Cersei, Brienne fights for Sansa, and those allegiances come before their own feelings.
"I'm not even sure that they would ever allow themselves to go to that place. There's no question you see that in this scene: There is more between them. But the way the scene ends, when she says, 'If this goes back, I'm going to have to fight for Sansa Stark, and I'm going to have to fight you.' And he says, 'Well I hope it doesn't come to that.'
"There's no question that if it comes to that, they'll both do it. And obviously she's going to kill him in an instant.
"Clearly there is something going on between Jaime and Brienne, and clearly it's something they can't act on. Maybe in a very secret moment. But they would never verbalize it."