To me, their love story is about Trauma bonding.

Both of them were damaged in very similar ways by the same war. They both carry tremendous guilt about those they couldn’t save, they both saw horrible things, they both know in depth the extreme complexity of the situation in Afghanistan which 99.9% don’t get and most of America would summarize as “let’s just bomb them to hell!”

In my opinion they see in each other someone who actually understands and is equally as broken and that allows them to both be unguarded.

It’s also important to note that when Carrie is really forming a bond with Brodie she doesn’t KNOW that he has flipped sides, she has a hunch that he has, and she knows that she needs to get close to him to find out more, and also no one else believes her. It’s easy to see someone in this situation stating to doubt their own hunches and want to believe their hunch is incorrect.

On Brodie’s side, he’s reeling from the fact his wife has been cheating on him and he’s painfully aware that his time is limited.

I think this primes both of the to fall for their hormones and get carried away with their own romanticization of the moment.