[0][1][2] I still can't honestly believe that people actually believe in brain sex. Swathes of neuroscience researchers have told you that it's disingenuous, it's a classic tool of projecting inferiority onto women, and it ignores the reality of neuroplasticity. The brains of taxi drivers are different than the brains of the general population -- does this mean that we consider them to be naturally born to be taxi drivers?
Your anecdote reeks of social conditioning. This is literally a social trope.
My partner and I make decisions together and rationally, figuring out the best course of action for the two of us. Miraculously, even with her lady-brain, we're able to come to a consensus and agree with each other before talking the majority of the time.
The differences in behavior can be explained by choosing the optimal strategy, rather than some deterministic brain chemistry.