As of now DM is wrong in Santu's eyes so the reason is so acceptable. I know Santu hides many things from DM but it is just because she loves him and tells him at right time. Santu has all rights to question DM because it is not about just hiding the truth but the entire base of their marriage depends on this fact. Santu might have lied to DM but the magnitude of Vishal's truth is nothing in front of all the lies . Common the girl has given every second of her life to make DM and his family and their lives happy ... We still don't know what is the truth so I dont stand by DM but he shall overcome n he will that I know ! All i know that Santu is right at her position.
Thanks for the update :)