"As You Sow ,so shall you reap".
Sameer had placed all his trust in Vishakha only to have it brutally shattered by Vishakha Somani plotting. There is no place for reasoning or cool handling of the matter anymore in him. He knows what the result of his pleading will be- a betrayal once again. The only option left with him is emotional blackmail and that's what he is resorting to every single time.
An unpopular opinion, Sameer's blackmail of Maheshwaris to take the to the Agrawal house midnight was correct, keeping in view his circumstances.
Imagine one day someone tells you forget your mother and you'll be separated from her forever. Isn't it natural that you'll go berserk and even do crazy acts, which later you might regret though. Same is the case with Sameer. Vishakha might have given birth to him, but after Nanu, Naina is his mother ,father, his only family. No matter what any relatives say, he won't agree to leave her at any cost.
Vishakha loves Sameer, but when it's time to take responsibilities , she escapes.
Question-paper stealing-escaped.
Delhi Dadi tortures Sameer- send away Sameer.
A true mother will fight for her child, beat him for his mistakes, but never let him be separated from her. That's exactly where Vishakha failed miserably. Whatever bond they had developed during Delhi phase has been broken due to her indulgence in plotting by Somani-Maheshwaris. And trust once broken is difficult to mend.
Whatever actions you see henceforth of Sameer may not be absolutely right, but he has no choice , he can't let anyone take away his mother-his Naina away from him at any cost.