Damn. Things were moving towards a happy, fluffy ending... And then one detail derails everything. There is no "good" solution. The only choices are to run away, hide the newfound knowledge or confess to it.
Guess the moral of the story is that destiny can find profound ways to mess things up.
Good thing the story did not have the incest tag. Probably that was the way the author intended for the story to be read for maximum impact.