ASR does not have to marry Khushi if Anjali finds out about Shyam and he escapes after blaming Khushi. All of them can simply cut off Khushi from their lives and move ahead. Any marriage will happen to hide things from Anjali and the family. ASR will be forced to take the step to hide things and not because the truth was exposed. Khushi cannot be blamed easily too as she was not the one running for cover each time Shyam came but the opposite. So directors don't try to fool us with stupid heartaches like that. The Shyam truth itself has been stretched beyond believable limits.
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