Personally, I think it goes down two ways. The chemicals behave in the brain as described, but the resulting behavior can vary.
Instance the first, like Puppy describes. Maybe it's a manifestation of cognitive dissonance. Convinced that OP is their at-long-last-discovered one-and-only soulmate and/or chance for escape/self-realization, the walkaway can't afford to give the LBS even the ghost of a chance. Can't endanger that French Connection, after all.
Instance the second, good sh*t is good sh*t. That sexual energy generated by the affair (EA or PA) gets channeled back into the marriage bed, too. For what could be a staggering variety of reasons.
You could possibly advance the argument that the first scenario is more likely to apply to women, and the latter to men. Although there's probably a lot of bleedover, depending on belief system and personality type.
"Show me a completely smooth operation and I'll show you someone who's covering mistakes. Real boats rock." -- Frank Herbert