Why is Montu annoyed with Amaya ?

He was hurt on being called a 'baharwala'. I understand his pain. Considering he has no parents and how helpful he is and more than that how the whole Benaras adores him, its rather insulting to be called an outsider.

But does Montu cares how his friend Uma treats the Mathur girls or especially Amaya? She does not even cover her hatred for the Mathurs. She directly confronts Montu for helping the Mathur girls. In his case at least none of the Mathurs insulted him and even if it was done because of them then he should consider the situation before being so judgmental about them. Sneha was not well that day.

My question is when he cannot take the responsibility of Uma's behavior, how can he blame the Mathurs for Rudra's behaviour ?

It was Rudra who used the word baharwala not the Mathurs. It was Rudra who didn't allow ramtu to go inside the house...so why all anger on Amaya...and why didn't he leave when Rudra was asking them to leave...would have left then...and had come later...as Rudra was not going to stay there forever. Though he is coming close to Mathurs, still not that close so that he can be called as part of family. He is just being quite immature...

Rudra called him self a family member and threw RamTU out of the house...

Mantu was about to go inside by force but just then the girls came and saw the whole thing but didn't go against Rudra, so he left angrily thinking the Mathurs insulted them...