Can some please help me figure this out?

Soo.. My former best friend came to my town 4 years ago. She came on my birthday. She came in fifth grade, and in 6th we became inseparable. She was shy, funny, and together we were a perfect pair. I was the down to earth, level headed friend. And she was the crazy, outgoing, silly one. When I was with her I was more loose and relaxed... Anyways to the point.. In middle school she started to care too much about popularity and boys. She became.. Well a whOle new person.. I didnt care, I mean I did, but for the sake of our friendship I tried to see her as the same person. Freshman year we started to fight... A lot. We fought about everything.. Her new "friends". Her constantly ditching me. Her new choices. And her dad. He parents are divorced and her mom ran away with her when she was little.. She stayed with her mom until her mom had to go to jail. Then she came to my town and lived with her dad. Once her mom was out, and got back into her life, my friend started doing bad things. Her grades started droppIng and she started having sex with older guys, sneaking out with them, and drinking.. I have always been a good girl. I do fight with my parents but it's not bad. I don't smoke. I don't drink. I don't sneak out. I am to shy to even talk to guys my age let alone older ones. And never have I even thought about drugs. And my friend has always called me the braniac because I am always on the a honor roll and I love to read. So I decided I didn't want a friend who does all those bad habits. I told her this. And all freshman year I didn't talk to her. I had made new friends. We were all close. She made friends with another druggie (who also was the same girl who almost wrecked our friendship Many times) and started doing drugs. At the time thought my life was perfect. I had great friends and still on the A honor roll. Mean while my old best friend was doing drugs, screwing 21 year old guys, and going to juvie. Lately though I realize how miserable I am. My "amazing friends" barely ask me to hang out.. And I have no one to tell anything to.. I miss her so much.. And it's my fault she's not even my friend. After I stopped talking to her she tried so hard to be my friend. She begged and said shed changed but I said no. She's now has moved on and has a best friend druggie and she too is a druggie but 4 years of friendship and I miss her. I want to tell her I miss her and want to be her friend again.. But I'm scared. Because I know if I ask for her friendship back then eventually I'll ask her to stop doing drugs and older men and I'll ask her to give up her old druggie friends. But I can't do that to her. I'm the one who walked out on her and when I left her lonely for year, she made new good friends(even if they do drugs) and I dont think it's fair for me to ask to take that away..am I being selfish? I miss her so much. And I want her friendship back so much. But can I do that? Can I just waltz back in her life, ask her to stop doing drugs, Smoking, drinking, sneaking out, screwing older men, and ask her to give up her druggy friends just because I want my old best friend back?