Post History
One character cannot explain their actions to the other without admitting a terrible crime, or without endangering the other. You can put even friends on the opposite side of a chasm; for example ...
Answer
#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/37344 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/37344 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
One character cannot explain their actions to the other without admitting a terrible crime, or without endangering the other. You can put even friends on the opposite side of a chasm; for example a reporter and a politician, or army general. A CEO and his son. This would be quite similar to (but different from) blackmail; only the secretive partner is basically blackmailing herself: She cannot let her secret be revealed, even at the cost of her friendship / partnership / marriage. Clark Kent cannot reveal himself to Lois without making her a hostage target of the worst criminals on Earth. Even when he did, she ended up dead, right? He had to travel back in time to prevent himself from the reveal. Or something like that. Going more to the dark side, one of your characters has a secret she is covering up: An affair, or a crime (from corporate espionage to murder), and the misunderstanding between her and her friend/lover/spouse springs from this secret. No plausible explanation --\> No resolution --\> everlasting misunderstanding.