I am confused

How can Sheetal pin Arnav as Arav's dad when Arnav himself has said to Khushi that he didn't have any physical relationship with Sheetal then how come its even possible? If the cvs wanted to go down this route then Arnav should have accepted in front if Khushi that they did share physical intimacy but were always careful so as not to end up with a kid when they were studying... Now it will come out as either Arnav has lied to Khushi before or Khushi doesn't trust her husband at all in either cases how can they have have light and romantic between them when both of them r upset with each other for any of the above reason.