divorce filing

My cousin brother wants to have divorce from his wife. They have frequent quarals. They have 8 years of marriage. No children. She blames him of not satisfying her of s*x and says that is reason of no child. She have diabetics and thyroid. My brothers reports are good. She seems to have extra marrital affair now. We don't want her to come back to brothers home from her parents house. We want to file for divorce. but she insists on coming back. how we can resist her legally from coming and staying here?