I'm 22, my best friend for the past 7 years is nearly 23. We met after our sophomore year of high school at a local barn we both rode at and became best friends even though we were very different. She didn't do well in school, skipped classes, eventually dropped out, dated a long list of shitty guys, couldn't hold a job, and was living pay check to paycheck. But she was a good person, was always there for me, never partied super hard or did drugs, worked at a doggie daycare and was always rescuing some animal off the side of the road. I went off to the military and then college but we still remained close even though I've been 200-300 miles away from her for the past 4 years except during breaks. She started smoking pot a year or two after I left, which was whatever since she only did it recreationally, then as time passed she started to rely on it heavily, taking hits every 10 minutes, not being able to eat or sleep without smoking. She had a nasty break up with her most recent ex, we had to go to court over it, and we mapped out a game plan to help her get her life back on track, but as soon as I went back to school she let it all crumble. She eventually decided leaving our hometown and moving to a different state with her sister would be a nice fresh start where she could organize herself and come back in a few months when she was on her feet. So during thanksgiving break I decided to drive out to see her for a night since her sister lived about an hour from my parent's new house. She had disappeared for a bit while I was getting ready but I figured she was just talking to the people who had begun to show up for the pregame and I'm not a big people person so I just stayed upstairs in the bathroom doing my hair. A few minutes later she comes up and tells me she was doing cocaine and that she only does it every time they go out and that it leaves your system in 3 days so I should be ok to do some. I literally just sat there holding my curling iron in shock before saying "I'm good. I don't need to snort coke to have a good time." And she got all defensive saying she doesn't need it it just "gets her ready" to go out 😒 After I finished getting ready I went downstairs and there she was literally snorting a line of coke off a plate through a plastic straw while her sister held her hair back. I was so mad and frustrated I almost felt nauseous. She just completely different from the girl I used to know, the one who I could call at midnight and we'd hop in my car in our sweatpants and drive down to the beach blasting music we used to listen to in middle school. She was so naturally bubbly and glowing and always had such a good natural shape. Now you can see her health falling apart, she is tired all the time, that night I went out with her she had sex with the guy who drove us home in her bathroom and I'm just done trying to babysit her and fix her life. She gets defensive if you try to tell her what she is doing isn't right and I don't feel like sticking around to watch my best friend ruin her life before dying.

Should I tell her I'm done or try sticking it out?