Anyone remember this story about the bet between the wind and the sun about who could get a man's hat and coat off first? The wind blew and stormed, trying to tear these off the man - but that just made the man tighten his grip on his clothes and hold on to them harder. The sun instead shone as bright as possible and warmed the man till he took his hat and coat off himself.
It's the same situation with Abhimanyu and Akshara but Abhi is too stupid to understand. He was gentle and attentive to her on the trip when they met and in the couple of meetings after. That's why she responded to him by developing feelings because obviously she's not used to such caring and kindness, thanks to a lifetime of meanness from her sister and the obvious blind eye the rest of the Goenkas have turned on Arohi's bad behavior. It was his warmth that made her open herself up to him emotionally.
But Akshara is very used to dealing with being ignored and with anger and taunts - it hardens her resolve because that's how she's survived all these years. By hiding her pain behind a smile and carrying on as though nothing is wrong. Abhimanyu has not once (in a sober state) tried to approach Akshara with kindness and gentleness. Since the first tilak it's been all about haranguing and domineering behavior with him. So of course she's closing herself up against his blow hot, blow cold toxic behavior the only way she knows how.
Abhi needs some lessons from the psychology department at Birla hospital. Instead of trying to cause her pain, he could try treating her with the warmth and compassion that first attracted him to her.