Manik viewed Nandini as:
His shining star: She showed him the way when he was lost. She always clarified things for him when he was confused, especially if it related to human relationships. She was able to see the goodness in him even when he himself could not do so. She showed him that being good need not be equated with being weak or vulnerable.
His protector: She protected him from himself. She controlled his violent streak. She was his conscience keeper, fearlessly pulling him up when he erred. If as a star she revealed the goodness in him, as his protector she purified his soul, making him a better person.
Now on that fateful night of Soha's death, Nandini, Manik's shining star and protector was unconscious. In other words, the girl who could have reasoned with him and curbed his rage was not in her senses. So how could she have been sure of the way Manik would have reacted to Soha's madness? Yes, he told her that he changes when he is with her, that she calms him down but then she wasn't 'consciously' present to guide him or curb him. In fact, her life was at stake because of Soha. There is no knowing for sure how he would have reacted at the thought of losing the one person who mattered the most in his life.
Even then her first thought was that he is incapable of killing anyone, let alone Soha, despite his friend's apprehensions that he could have. It is only after she saw the footage did she believe that he could have 'accidentally' and not 'impulsively' or 'deliberately' killed her. Is this really then a test of trust? I don't think so.
Did she believe that Manik is a murderer? No. Did she believe that Manik could have deliberately harmed Soha for daring to harm Nandini? No. The old Nandu would have, the one who had believed he had sent the goons against her or that he had tried to kill Harshad for harming Cabir because she did not know or understand Manik well at the time. The new Nandu, the one who has seen umpteen instances of Manik's goodness and change of heart would never think Manik would deliberately harm another human being but then she could not fully rule out Manik's hand (unintentional as it may be) in Soha's death.
So how then can this be seen as a test of her trust in Manik? If Manik had said he had no role to play in Soha's death and she contested it, then he could have been furious with her for not trusting him. That was n't the case was it? So why was Manik behaving so unreasonably with her?
This is where expectations come into play. Manik was so confident that Nandini will defend him stoically, even if she was unconscious throughout the incident and her ambiguous comment threw him off guard. As if to add salt to the wound, the woman whom he detests the most ended up setting him free. So when expectations are high, disappointments are also bound to be high. He was expecting to confess his love and celebrate his first valentine with his girl and ends up being 'betrayed' her. So his anger and frustration is understandable but to stretch it to a trust test which he deems she has failed and 'hate' her for it does seem to be too extreme. Manik needs to hear the voice of reason - read Cabir - soon.
They can stretch the reconciliation and reunion if they want by bringing in factors such as the new teacher or the new student into Manan's equation but this particular misunderstanding is too flimsy to stretch for weeks.