How can I stop my moms abuser?

I am 17 and I live in a different province from my mom because of her abuser. He has abused her for the past 2 years to the point of almost killing her. She has slept in ditches to avoid being near him but won't leave him. I want to be with my mom but because of this guy who has been in and out of jail for these 2 years for domestic abuse her whole life suffers. He brings her into a lot of drugs and booze and has some really bad addiction issues because of him. I have tried calling the cops but it just makes everything worse and now because my mom bailed him out of jail with her house as callatoral if he does get arrested she will lose the house and that would hurt her even more then he does now and she would despise me. She has contemplated suicide before. I just really want to know what to do because this is really killing me inside...