My guess

I think Pari might leave a letter telling she can't act as his fiance anymore and leave by the time Geet comes back since she has come to know something is in between Maan and Geet and then since Maan doesn't have much of time, he might force Geet to become his fiance....Pari might give a clue that she is leaving because she thinks they both should be together or something like that and Maan might blame Geet because she is responsible for this and might force her to become his fiance or rather leave her with no choice by ordering she has to do it because this will affect Dadi's health

we might then have a track where Maan might always be around Geet or romance with Geet telling that Dadi shouldn't suspect or it might be that Dadi herself might be doing something to make them stay too close

It's quite possible yes what you're saying , but whatever the reason may be that Maan forces Geet into this engagement, I want Maan to be aware of Geet's past ..........doesn't have to know the names necessarily, but he should know, I feel Geet cannot go so close to Maan now that she knows what she feels for him OR what his feelings are for her, without telling him, otherwise it can look like cheating to Maan later on or misunderstandings can arise.