How do I deal with this "friend situation" with maturity?

I had a best friend last year.
We had everything in common. She wasn’t always my friend because I was the “new kid”, but within a week of knowing her she was already at my house every other weekend and we knew every detail about each others lives.

This year, there was another new girl. We accepted her into our group because we all had things in common.
Over time, this girl has taken my role as “best friend”. They act like sisters and they completely ignore me.

I’ll see them in the hall, and while just a week ago we would smile or acknowledge each other, she just walks by now. Both of them.

This girl has gotten her into drugs too. She smokes marijuana and I don’t know if cigarettes, but probably. God knows what else she’s done with this girl. She and the new girl have also been accepted into this gang of “bad girls”. They get into fights, have sex, do drugs, what have you. Whatever constitutes a “rebel child”, she’s become it.

It just bothers me that she’s treating me like a loser now.
Like because I’m not doing drugs and having sex or presenting myself with the stoner “chill” attitude and the slow, uneducated, hippie lingo.

They just act like sisters and I’m not part of it. I’ve known her for longer and we were great friends last year…now they act like I’m annoying.

I’m just not sure what to do or say about it. If I tell her I’m feeling left out, she’ll be offended and they’ll no doubt go behind my back and call me a needy loser.