I know a lot of us are annoyed with Thapki's 'lectures' but honestly the long rant today was much needed on her part to get all the pain out of her. We need to remember that she is a girl who lost everything, even her name Vaani, due to something she calls her 'imperfection'.
She is someone who has been rejected time and again because of her stammering. Dhruv was someone who was willing to overlook this and accept her. This made her dream for a better life again.
This dream was shattered brutally by Vasu as we all know and by Bihaan as Thapki knows at the moment. Bihaan, while trying to hide Vasu's reality, tells everyone that his motivation behind doing what he did was to make sure that his brother did not marry an imperfect girl thus taking another stab at the rejected heart of Thapki.
Thapki did not love Dhruv. She was infatuated with him maybe but what meant the most to her was the dream of having the perfect life that had been shown to her by him. And it is the pain of facing yet another rejection that is killing her from within frustrating her and letting her take out her rage against the world on Bihaan.
Today's rant was important as it let everyone, especially Bihaan know the extent of Thapki's hurt and the fact that the damage done to her is irreversible at the moment.
Hopefully, after the cliff drama, Bihaan and Thapki try to make a cautious new beginning for themselves. Bihaan has already come to realize that Thapki means something to him because of Dadima's comment. He will help Thapki come out of her grief an in return, Thapki will help him get the care he deserves and become a better man.