Twilight in Delhi Lesson Plan

What does Ashgar mean when he says that Begam Nihal "lost her reason" when they were children? What happened? How is this another example of the patriarchal society of the time?

Begam Nihal suffered a mental breakdown after the servant, Dilchain, birthed a son that was rumored to have been fathered by her husband, Mir Nihal. After consulting some traditional doctors, Mir Nihal sent Begam Nihal away to recover at an uncle's house. Ashgar and Begam Waheed accompanied her. Eventually, she was deemed fit enough to return home and Mir Nihal came to collect everyone. The patriarchal society is again demonstrated in the extramarital affairs of Mir Nihal. He can have a child...