First I thought she was the spoilt brat and must have done something major for them to fall out but the way the milaap happened they don't seem to have a fall out
Now I think may be it was because Anuj was so desperate in love with Anu and felt helpless and devastated that he spiraled down and went on the wrong track for a bit, or even tried to kill himself and malvika saw all his suffering and so he did not want to open that chapter in front of Anu yet because it will bring all the negativity back. Malvika may have hated Anu because of her brother's suffering so that could be another reason.
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