I think we are all aware of the fact that Ekta has a habit of creating mounting suspense in her dramas, esp. KSBKBT, only to dissipate it when the viewers are tired of it.
Nothing is wrong with Sahil's morality(please dont take me at my word, i may be wrong but that is just my viewpoint). Its possible that in some previous episode, Mohini might have bribed him about business and stuff and now just blackmailing him to get the required money to pay, probably, to her husband(not Harsh but we know she has had many before she came to Shantiniketan) so that he keeps his mouth shut in front of the Viranis. Sahil may just be a weak wax in her hand to achieve her purpose. Gautam & Karan are already against her in the Savita-Tulsi episode. She might have said to sahil that one night you were heavily drunk and then we did this, blah blah blah.
These are my conjectures. what do you think of them?