Restitution of conjugal rights

My sister's marriage was held 10 years back. She has 1 daughter of 9 years. From last 2 months she noted some changes in her husband's behavior. Now, 20 days back her family came to know that her husband lives with some other married women as live in relation. Her in-laws are in support to her and tried to convince there son to leave the wrong path and to stay with my sister and her daughter. But Now he stay in the same house at night in separate room. No talks held between my sister and her husband. Some times he tortured her by shouting and some times he told her that "tu mar jaa....jahar kha le....finyal pee le...mai laa kar deta hun....bla bla". he always used to say that "mujhe tere saath nahi rahna, mujhe uske saath rahna hai", he also told this same thing to his parents also. He also not paying single penny to my sister and also not paying school fee of his own daughter. My sister don't want divorce from him also. Please advise what to do. One more thing he is regularly in touch with that lady.