My sister's boyfriend cheated on her with numerous women and she is not able to break up because she loves him so much. What should I do?

Anonymous
My sister's boyfriend is a complete jerk ugly asshole. He treated her like shit he cheated on her many times and when she confronted him he blamed her for being insecure and would ignore her and hurt her a lot. And i told her to break up many times and to love herself i encourage her a lot to move on and have a peaceful happy life but she isn't listening to me. Its her life but i can't see her getting hurt and loose her self in the process. She was a strong girl with an amazing personality and kind. Now she has changed completely, whatever her boyfriend does is right according to her and she has become very weak and spent most of her time trying to impress her boyfriend. Her boyfriend would tell her to be more like other girls and kept talking down on her and she really thought he was right and she tried to change herself in many ways which made her become weak, shy, mean and oppressed. And she gets offended whenever i point out her boyfriend is wrong and these days she doesn't even share about her boyfriend wrong doings anymore. Even when he cheats she doesn't get angry with him anymore just because she can't break up with him. I can't tolerate it anymore. But she stops talking to me whenever i utter a bad word about her boyfriend , she says im insulting her choice of boyfriend which means im insulting her. She was never like this before she usually asked me for advice and listened to me and she has her opinions too now she isn't opinionated anymore. She was a little bit of introvert before but she managed things well but now she has become more introverted and aware of what people would think of her words etc, in short she is being oppressed. What should i do?
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she had her opinions but now she isn't opinionated *
My sister's boyfriend cheated on her with numerous women and she is not able to break up because she loves him so much. What should I do?
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