TW drugs overdose suicide attempt abusive relationship

For starters , I am not looking for a friend or romantic interest in anyway, I ask kindly that you do not message me with that in mind. I have nobody, and I am so scared and sad and just want to talk about this.I just turned 19, My almost 21 year old sister is homeless. She was kicked out by my mom nearly 3 years ago after years of them fighting and my sisters drug/alcohol abuse. She moves around places, sometimes living with her friend for months or her abusive 47 year old mans bf. The last 6 months she came to me with nowhere to go. I was terrified and didn't know what to do, my mom wouldn't let her back in and offered me no support at all. I was alone. I am alone. I started staying up all night bringing her hot water bottles blankets food water, things like that. Most of the time she was passed out and that always stressed me out. I worried of an overdose. Recently my biggest fear came to life, I walked outside and saw her in a weird position. I walked over thinking it was just her usual state, and that when I tapped her she would immediately awaken like always. But she didn't. I picked her limp body up and her eyes were open and completely white, the colored part was rolled into the back of her head and blood was coming out of her nose. Her face was colorless and pale as an actual corpse. I couldn't move for a moment I just stood there tapping on her face calling her name, when she didn't respond I ran into the trailer and screamed at my mom to call an ambulance. I ran back, checked her beathing and pulse, both were slow and abnormal. I was prepared to do CPR but the ambulance got here before I needed to. The police came first and were immediately judging me. "Why don't you let her in, why are you letting her sleep out here?" My sister woke up and I told police that she was having a seizure and overdosing. She was restrained by 12 cops and forced to go to the hospital, all while she screamed loudly "YOU CAN'T ARREST ME NO" and also screaming my name. I told her she wasn't being arrested and so did the cops but she was disoriented and still thought otherwise. After a short trip to the hospital she was given narcan and almost immediately released back to my house. I stayed up all night scared checking on her. She recently she went back to her abusers house. I told her to message me and she wasn't so i went to his house and they answered the door together. If she didnt go on her on free will this would look like a hostage situation. he is drunk right now. i'm scared and idk what to do. If i call police i have no proof of violence and they wont do anything , i risk making her abuser more angry. If I hurt him I go to jail and that changes nothing. People keep telling me im not doing enough and that i need to be helping her, how ? how do i help? She has BPD , depression, shes suicidal and the night she overdosed was trying to kill herself. WHAT DO I DO ? WHAT DO I DOOOOOOOOOOOOOOOOOOOOOOOO,. My mom dont care about her or me , i have noone. People keep telling me to call cops, you dont think i want to? They dont do shit i have been in this situation countless times. Domestic abuse hotline? they dont help. Nobody will help until shes dead , she has mental problems and she needs professional help but people keep telling me its her fault and she chooses this and that i cant save her. THATS NOT AN OPTION FOR ME.