I am obsessed with my best friend and other people and its killing me

I study in the best university in the country. I worked so hard to get here. I am alot of goals that I have to achieve. But since the past 7 months I have totally become an other person. I am uneasy with new people, I doubt myself, I get angry and all of my thinking is black and white. I will like or you can say "love" a person at one moment and the second they do something not according to my expectations I will hate them. I did the same thing to my best friend months ago because she talked behind my back to a third person and because she was so controlling, she would repeat over and over again that she is the leader of the project group and that we should listen to her. She used to backbite about our third friend and I didnt liked that. But I couldnt really tell her that she was wrong. I have been thinking alot, I know that she made mistakes but I did too by not being straight forward. Instead of telling her straight to her face that she is wrong i gave her silent treatment, which was wrong again. Because after doing that I was the one who felt horrible. She was okay, she made new friends and entered a group. She was generous enough that she asked me to join the group too because i said i was sorry and that I was "depressed" and that is why i stopped talking and not even then telling her the actual reason. After all of this, we become friends but she would say horrible things whenever she would get a chance, she would tell me that I had done wrong, I have apologized to her since that moment everyday, 24/7 on calls, texts, facebook, snapchat, emails and in person. I really needed a forum to discuss my situation as the psychiatrists in my area (I went to one because i was so sad and cried 24/7 for that girl and did not wanted to live anymore because of the guilt) think that every situation that a young person is in is because of relationships, you now boyfriend girlfriend issues. That doctor kept digging about my love life and didn't listened to what i was trying to say. I payed a very heavy fee as they charge so much. I have studied alot on the internet to get to know myself better. Borderline personality disorder BPD, is the first thing that matches my personality. I think in black and white, I get so angry that i want to hurt the person in front of me by my words that I regret afterwards, I am depressed, I have favourite persons. I think my friend is my favourite person, I spent around $3000 in the last 7 months to make her happy. so that she would stop calling me aggressive. I have not been angry with her in the past 7 months I have not raised my voice and she doesn't even know about what I am facing yet she calls me aggressive. I searched alot about her too and found out that she has a passive aggressive person because all of the traits matches hers. I have tried not to blame people for the stage i am in today by calling her passive aggressive only is not going to be a solution so I have tried to study myself too. But the thing here is my fiance, I have been with him for 6 years now, everything is so easy with him, he listens to me and tries to make me understand what i can't. He told me that that girl is my safety net, is she goes i will be alone, though i won't be as now we are a part of a bigger group. I can't think properly, I think about her every second of the day, that why is not replying and talking to me like she used to. I discovered that she is not the only person who when dont reply to my text in time i feel anxiety, fear and a sense of abandonment. I called a friend who is in our batch, she is a good friend of mine, she picked and told me she was with the family and that she will call me in a while, i waited for 3 hours and those 3 hours were like a hell. I assumed so many things that maybe she hates me etc etc and then i called her myself, it was pretty late and she told me that she totally forgot and talked to me just like she always does. So does this mean that i have alot of favourite people? or that i am obsessed with people? my emotions depend on my best friend and other people. The university starts in about a week, I am feeling so scared. I will feel jealous like i always do when I see my best friend talking to other people. She says horrible things for eg, you were my best friends but i have more friends now so my love for you is now divided between all of them. I love her for some days then after she ignores me i hate her but i cant say anything then the cycle repeats. I am feeling crazy, why do i do this? I would like one thing then after a day or two I won't. this applies to every action of mine. Am I bipolar? or narcissist? or have BPD? What is my issue that I can't take my mind off of her? Why do i feel the need that I need to make her happy, to explain her stuff to call her to text her to praise her, when she treats me like a normal class mate? Why is she so important to me? How can i undo this obsession? How can i not care about her the way she doesn't care about me? And how can I handle myself? my black and white thinking? People are either angels or demons. Nothing in my life is between the scale of 1-10 its either 1 or either 10. there is no 5! why do i expect so much? I wanted to be a memory champion but i have wasted my summer vacations thinking about my friend about people. If she calls the day goes perfect and I am happy, If she doesn't reply or talk to me the day is the shittiest. I will cry and feel weak. In my experience when i waited for the other friend to call, I felt the same, I felt sad and went through my texts and thought about our last call and really thought hard that what had i done that had made her unhappy and that now she is not calling and ignoring me. My grades went down in the last semester, I lost weight, I was weak, I stopped laughing, I was depressed, I didn't know how to act around the new group and i just wanted my best friend all to myself. I don't know how i am going to go to the class now. I am scared of everyone. I felt very uneasy sitting in the new group and i am scared of them. Whenever I talk to my best friend, i imitate her, I speak like she does, I don't know why i do that but i think i do this to make her happy. I am so fed up my myself that i want to kill myself. I am not able to understand myself. who am I? Why can't i be normal like others and not depend on others? Please help me. I try to make myself understand that it will be easy, just take the classes and come back home and do other stuff. But I spent the entire summers thinking about her, what will happen when i actually see her and worry about every little thing. I am trying to shut my self up right now i am scared that i will take wrong steps and maybe end myself. I do know that its not worth this but i just can't get this off of my head. And this happens with every person i get close to. If my fiance doesn't reply I assume things. And i do think in black and white. I wanted to change university but i can't as my parents have worked so hard to get me this far. I am not confident at all. I dont know how to talk to people. I check facebook, my bestfriend used to tag me as i was her only friend , now she tags other people from the group. I don't know what is that i want, she hurts me, I hate her for that, but i love her and i want her. Am i really a BDP? please tell me if you think i have something else. I have 1 week to get myself together or else i will lose my self.