I am terrified

I have watched my sister go down the path of drugs and it turning BAD. She overdosed on loritabs and died 3 times in the ER. It was to the point that she didn't give a damn if she died. She would inhale all of my cans of hair spray and lie about it. Anything she could get her hands on that would give her any type of high she would figure out a way. It got to the point that my mom had to send her to rehab for almost a year. She sat me down and turned on music and said "when I die I want this song played at my funeral". She told me she wished nobody revived her. I have completely lost this person in my life because of her choices. I can no longer have her in any part of my life because she destroys everything. Just because of freaking drugs. I can't do this with my boyfriend. If it spirals out of control like it did with my sister I won't stay around. I am so terrified because I love him so much and I don't want to see this ruin his life. It hurts me to know he's doing it, but recently it's like he's on edge if he doesn't have it. And I know his friends detox off of it when they run out. He's doing it all the time, like he craves it. Give me advice please😥