I wouldnt blame Durga. Her best friend was not there for her when she needed him most. She got an email. She got taunted. Did he try to make any contact. Yes we viewer's know we need to hear Dev's story. Why. Dev is the male protaganist. So he will come out clean.
But before that Nithya needs a strong reason to trust Dev once again. She had trusted him, trusted him blindly but he was not there for her when her family was destroyed by his family. His silence was with his family. So according to her he should go down with his family.
Even in that anger and frustration Durga cries taking revenge from Dev in her personal moments. Second though she is plotting this and that , her conversation with Dev is not faked. She is genuinely comfortable with him that is why Shaurya is more irked because unknowingly Dev- Durga has a comfort level with each other.
She cringes in Shaurya's touch , but had no qualms taking Dev's arms. Even when Dev danced with her or held her hand or their hands touched each other while trying to change channel in FM there was comfort in her eyes. Taking revenge from Dev is difficult for her too as she has emotions attached.