The person Arnav loves most in this world is his sister and he would do anything to protect his sister, he even went to tell her that her husband was betraying her. But when she was pregnant after so many years of marriage he could not hurt her when happiness came to her after so long.
Arnav is a strategist and in his thinking, Khushi was causing Shyam to betray his sister, so he would eliminate the cause. By his marrying Khushi the cause was removed and Shyam would have no choice but to stay with Anjali and keep her happy.
While Arnav has been very rude to Khushi he has never deliberately caused her harm or injury, emotional distress is a major part of love, its not love if it does not hurt.
Most important Arnav loves Khushi and this way he can justify marrying her to himself. Yes, he is angry with her, he doubts her, but he is emotionally disturbed and not thinking straight. Seeing her with Shyam was a big blow to him but he still loves her and that love with slowly surface.
Have faith in love, it will triumph.
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