How can I help my sister leave an abusive relationship?

Hi, so my sister has been with guy for nearly 4 yrs, hes always been controlling to a point and the maybe a ur into the same he got extremely bad, like he wouldn't let her see her family or spend time with anyone best him. And then it got worse, he started hurting her, leaving bruises, biting her , screaming... show more Hi, so my sister has been with guy for nearly 4 yrs, hes always been controlling to a point and the maybe a ur into the same he got extremely bad, like he wouldn't let her see her family or spend time with anyone best him. And then it got worse, he started hurting her, leaving bruises, biting her , screaming as loud as possible right in her face. Then our mom passed away and he changed into a totally different person . And he was like that for a year, and recently all of a sudden he fell back into his old ways, and has just been awful to her again. And on top of all tha hes super lazy dont want to work and muches off our elderly dad and my sister. But she never ever leaves him, no matter what he dose? And she started cutting herself!! I dont know what to do? How can I get her to realize that she needs to end this relationship?
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