Friend removed people she cares about, why?

I was hoping someone could tell me if this is common behavior. Found out my friend has been using meth or some other substance for a while and never noticed til recently. Behavior gave it away when she started to have massive mood swings, be calm, then intense rage over little things, to extremely calm again. But I'm curious because she removed her best guy friend from her life, he did everything for her, if she needed something he was there for her. Then did the same to her best girl friend weeks later, she always called her her ride or die and told her everything. Is it common to someone hiding an addiction to remove these people from their lives? Guy friend was around for a while and again went above and beyond for her knowing she struggles and needs help, her girlfriend has been her best friend for over 8 years...