Dev is always and will always be a mamma's boy. To him , his and his mother's happiness is the same. Even during NATASHA's time when he was constantly looking up to his mother for guidance, she always told him that she will standby by him in whatever he decides and her happiness lies in his happiness.
Today he is extremely happy that he found his soulmate in Sona and like any other boy who never asked anything for himself, he is skeptical in telling his mother that he wants sona and dreams of living his life with her. In a way he was not yet prepared to break this news to his mother,when he was forced to admit his love to Eshwari due to her actions. once done with it, as he always believed that she will support him in all his decisions, he firmly believes that his mother is genuinely happy for him.
Like he said, Eshwari always treated Sona like one of her own daughters, but the fact that is unknown to him is : Eshwari can never accept anyone for her son because of her own insecurities.
Like Neha pointed out, the more he likes sona, the more the mother will be against her.
If we carefully look at the suicide promo, its neither Dev nor Sona about whom Eshwari was thinking about. She was pondering about her own self... her emotions and her behaviour. She is very well aware of the fact that Dev is searching for happiness on her face whereas she is not happy from within. she is in state of emotional turmoil and for once, Dev is unable to comprehend it. Dev feels he knows his mother but the person with real emotional bonding with the mother is Neha and not Dev. Neha knows her mother like the back of her palm as depicted too often and she is vocal about Eshwari's shortcomings.
the suicide attempt will serve as litmus test for both Dev and Eshwari to do a reality check on their bonding
