Peace, that's a really good point about the engagement sequence! There was a lot of ambiguity about Kunal's feelings. Kunal even tells Shweta something like, you can't separate Kuhu and me, which is strange because the whole point was for Shweta's appearance to cause drama and break the rishta. 😉 Even if Kunal didn't know Meenu had orchestrated this on purpose, he should have seen the opportunity when it presented itself.
The thing about that phase is that neither Kunal nor Meenu wanted it to get as far as the actual shaadi. They wanted the Maheshwaris to cut it off much before that, and cause such a huge rift between the two families that nobody would ever agree to let Mishti and Abir pursue their relationship. She expected Kuhu to react like Mishti did when she broke the GD, so they could play the victim but Kuhu didn't oblige, and Abir kept smoothing things over when she tried create deal breakers, so the natak just kept extending, the stakes got higher, and Kunal got more and more uncomfortable with it as time went on.
There's a great scene the morning after the bachelor party when Kunal laments to Meenu for almost having revealed the truth to Kuhu and Meenu says it's okay and it actually worked in our favour because now everyone believes that you love Kuhu very much. Kunal's reaction to this is definitely worth noting! It's similar to when he fights with her over the prenup and asks what was the point of ruining his, and more importantly Kuhu's life? She retorts with, I know you never cared about Kuhu and once again, you see this conflict on his face, where he knows it isn't the truth but he'll never say so out loud.