Wow, really? Knowing mother from Xiao Bai's memories, she seems to be weak willed, at least, whenever she was around town or when his father was around. She seemed to be a bit emboldened whenever Xiao Bai and her were alone. So, something did happen. Maybe she called or sent a letter to him announcing their breakup and reason being that she found another man, but was actually coerced into it.