How do I help/convince my mom to leave my abusive stepdad?

My mom has been with my stepdad for almost 10 years now. I was 8 when they started dating and I can remember them fighting over the phone all the time and I would cover my ears and cry. He lived a few states away from us. I wished they would just break up. At some point they did, but then got back together a few weeks later. From then on everything seemed fine. My stepdad, I’ll call him steve, would buy me and my younger brothers toys and play with us constantly, and even though things seemed normal, I always knew something was off about him. Eventually my mom made us move states to live with him, away from all of our family and my bio dad. It was rough at the time, but since then I’ve found my wonderful boyfriend and many other friends I wouldn’t trade the world for. Things started to get sketchy. They were constantly fighting, having screaming matches that would have me in my room rocking back and forth on the floor and ripping my hair out. My mom has always tried to be a friend to me and not just my mom, which I’ve had mixed feelings about, but she would always run to me to complain about their fights. She’s been doing this since I was 10. She’d run to my room, lock the door, and hide from him. He would come running to my room and kick my door down, one time he got a screwdriver and took my entire door off the hinges just to get to her. He’d start yelling at me, telling me that my mom deserved this and they would yell and try to get me to take sides. I would just scream and cry and yell them to get out. It didn’t really get better. Things got to the point where Steve would throw things at my mom when they’d argue. It started with him chucking the tv remote full force at her head, and she ducked out of the way thankfully. Then, he slammed the door on her face while she was trying to get past him, leading to her scream crying as she held her nose. Then, he picked up a full laundry basket and hurled it at my mom. I never saw calling the police as an option because my mom didn’t want me to, and I didn’t have anyone in my life telling me she was wrong. This carried on for years, and my mom eventually opened up about his alcoholism and how he’s serially cheated on her and has open hand slapped her before. When I was around 15-16, one of my brothers must’ve done something to irritate steve, because he chased him to his room and began kicking the door in, which completely broke the bottom of the door. My mom ran to him and screamed at him to stop, and he instead turned around and began beating her. I jumped up and ran to them, literally having to use my own strength to pull her away from him. I almost got beat in the process. After that, me and my brothers ran into my room with my mom, where she always wanted to hide, and Steve busted my door down and began yelling and screaming at all of us. I told my mom I was calling the police and she lost her mind telling me not to and that I was gonna get her killed. I reluctantly listened. As of now, their relationship is just dead. He still berates and bullies her, watches porn in front of her and tells her he has to since she lost so much weight and isn’t attractive anymore, has still continued to talk to women behind her back, and overall is a shitty guy. My mom keeps saying she’s “done,” but refuses to do anything to get away from him. For reference, she is a respiratory therapist at a large hospital. She makes well over enough money to be able to afford a place on her own. She tells Steve she’s gonna serve him divorce papers, but never does. She tells him she wants to split, but he says no. He wants to stay because he’s convinced we need him and can’t live without him and he thrives off that. Really, he’s a milk man (literally) and he’s just a nuisance to live with. My mom has not filed any reports, has not gotten divorce papers, will not stand her ground and tell him to get out, and will not take initiative to maybe even find a new place for us to go. She just comes to me and cries saying she just loves him so much and doesn’t know why. And that she feels bad for him. I’m so fed up. At this point, he’s abused her, tormented her, and is even to the point now of threatening to hit my brothers and has multiple times told them they can “take it outside” so he can fight them. The line was already crossed the minute he started mistreating her, but the fact that now he’s targeting me and my brothers as well should be all she needs to pick her ass up and do something. Yet she doesn’t. Shes started not asking him to cook dinner, not asking him to help take my brothers to and from school, or to go to their sports games, take them to important appointments, to clean, now instead she asks me. I cook dinner for 6 people 5 days a week now. I clean the entire house. I constantly drive them places and spend lots of money on gas. Im tired of it. Im 18 and trying to move out with my boyfriend soon to hopefully get away from this mess. I wish there was something I could say to her to get her to snap back into reality and LEAVE. I want to mention that we are not actively in danger, he hasn’t hit her (not that he’s not capable, he still is) in 2 years. If we left, he’d be butthurt but wouldn’t stop us. He just thinks we need him and won’t leave. Is there anything I can say to her? Should I just focus on myself and get out with my boyfriend? I’m beginning to grow resentment to my mom for keeping us in this situation because she is complacent. I’m just so done.