Hmm I do think they both still trust each other. Manik had enough trust in her to know that if he stepped back, she will pull him towards her. He trusted her enough to know that she will always be with him. Yet it was because of his this trust that he had to be somebody else- his monster self and cover the real Manik to break up with her. When he said "rok lo mujhe" , that was the only slip in his facade .
Nandu too believes the real Manik , she still does. As today during the shadow scene - she called out his name, she is familiar with his essence and presence. It is her trust that she channeled her anger at him and confronted him. Even in her anguish she trusted his comfort and reached out to him today. What she didn't and still doesn't understand is his mask- Monster Manik, it pricked her self-respect. She detested this fake Manik and doesn't trust him.
Manik made a choice not because he doesn't have faith or trust in his true love but because according to him his promise of years and duty of protecting Dhruv supersedes everything as of now. Nandu too still trusts Manik , as evident by her strong emotions for him even after all this. But she just doesn't care or know the masked Manik.
The trust was between the Nandu and real/normal Manik. But at that point there was no Manik just an evil Monster.
What they both lack especially Manik is trust in himself. He just doesn't trust himself to be worthy of her love especially when it means stripping away the joys of someone he has been protecting.
Even in hate they trust each other, they always have.
But this break was needed because they both need to grow up, without this Manik won't have understood his unhealthy relationship with Dhruv or his flaw of always sacrificing himself for his friends. Nandu too needs to trust herself and not look at fireflies or the metaphors to be sure of her feelings.