Someone suspects. A letter is found. A GPS tracker reveals a lie. The threat of exposure becomes the main antagonist. Often, the couple fantasizes about running away—the "escape fantasy" is the forbidden relationship's dream sequence.

The difference: The struggle is against the world, not against each other's will.

Too many stories end with the couple triumphantly together, ignoring the fallout. A great forbidden romance shows the collateral damage—the betrayed spouse, the disowned child, the lost job. That pain gives the victory its weight.