Nothing hurts more than being disappointed by the single person you thought would never hurt you.
Today when Kunj heard twinkle confess to knowing about the whole purvi-manohar deal in front of everyone, I saw something break in his eyes. The look of disbelief he had on his face clearly shows how much this affected him. It has nothing to do with what twinkle did being right or wrong to him. It dealt with the fact that he thought she would at least consider him important enough to share this piece of info with him. He just stood there like a statue on knowing that the person who has grown so dear to him, hid such a big thing from him. At such times, one is no position to weigh the pros and cons of an action. He was simply in no state to assess twinkle's actions. He was already broken, family is kunj's weakness and seeing his dad fighting for his life shattered him.
Even if that's the case, he stood firmly by her when everyone else was raising fingers at her. Even yuvi's fake video couldn't shake his trust on her. He might blame her for hiding this whole thing from him and may even hold her responsible for this turn of events but he will always trust her. He knows she will never do anything that will lead his family into harm's way.
This quote holds true for them,
"Love is weakest when there is more doubt than trust but love is strongest when we learn to trust in spite the doubts."