I still think it sounds like her using you as a last resort when she feels like she needs something or has no one else at the moment. But how would I really know? I've never met her. It sounds like she probably doesn't have many other real friends other than you, as you have stated. So she probably feels lonely and frustrated, along with low self esteem. This is when she probably takes things out on you and pushes you away. She also may feel bad and guilty about yelling and acting on her impulses after she realizes what she has done. I still don't think that's something a real friend would do. Unless maybe they were under the influence. You said she drinks a lot and it's probably to self medicate, along with ya'all being only 18. As for me when I would drink a lot when I was younger, it would actually help me focus. I could do something for hours. Later on in life it seemed to make things much worse. Couldn't focus on anything. Then again in my later years of drinking I was drinking so much more. Up to three pints of hard liquor a day. So there is a big difference there. I would like to have friends but it is hard when you isolate yourself. Maybe it's the same for your friend. I don't know. Anyways, was kinda losing my train of thought so I hope what I typed came out the right way and I hoped I answered your questions.