Why can't abir/ parul tell mishti the truth?

I know its a serial and needs some stupid decision from characters to move the story forward but just think about it.

I know mishti would have not gone along with their plan and would have rather told them to reveal the truth to kunal. That way if abir doesn't agree atleast mishti has option to walk out from the relationship without feeling betrayed and abir could have escaped from some guilt of hurting her purposefully.

And Honestly, KUHU is walking example of how she still has name and respect from her family and varsha inspite of her illegitimacy. At one side they talk about nayi soch and still talk about illegitimacy stain. I know its hard. But didn't mishti accept naman's past deeds? kuhu accepted varsha? abir accepted mehul's truth? Even Kunal gotta face the reality. The sooner the better.

What do you think?

Mishti already knows the truth.

She thought meenu has hidden it for some purpose.

But here it's used against her only