Friend or Foes for life

Growing up I didn't have many friends. Or atleast not that many I could trust. When I hit my sophmore year of high school, these two girls took a liking to me and we started hanging out a lot. We were inseperateable. This is another time where my life started to fall apart. We used to hang out every night, sometimes till 3 or 4 in the morning. We hung out mostly with older men, drinking and smoking weed. I mean, I was trying to fit in with the only girls that actually wanted to hang out with me, and my home life wasn't the greatest. The one girl actually met someone so it became just two of us. For years we did the same things pretty much over and over again. She always had my back if we were to get in trouble, just as I would have hers. I used to wonder sometimes though, I noticed sometimes she would talk about me, in front of me and behind my back, about some of the things I was doing. It was like she was adjusting to who ever she was around. Sometimes it was hard for me to tell her things in confidence because again, depending on who we were around she would say something. I know it sounds like she wasn't being much of a friend, but in reality she really was. I could always talk to her about anything and we always had fun. We looked out for each other when we would run away or go out late. To this day I still talk to her and we're still good friends, but when I need someone to talk about stuff with that I can't talk to anyone else, I always find myself asking.....if I tell her, will she tell someone else?