Will my ex come back even though she cheated on me?

I have been with my girlfriend for 3 years and it has been a long distance relationship. We got together right after high school and I went to a college 2 hours away. Her mom died when she was young and has some disorders but doesn't go to therapy. Her father does not hing for her and her brother and sister aren't really there for her. She only really has one true friend but isn't that stable to talk with. I feel that I am the only one that truly loves her and understands her for who she is and she has said that before. The first year she told me she kissed somebody and didn't know what to do if to stay with me or not. Then after awhile she stayed with me. The next is I start liking a girl in college and I don't know how I truly feel about my girlfriend. That went on for a couple of weeks but I never slept with her. I came back to my girlfriend and lived with her over winter break and at the end of winter break, she broke up with me and went to a college that was an hour away from mine. She would text me all the time saying very nice things. Then later on she found a guy and dated for like 2 weeks and the guy thought she was crazy. Thats when she finally came back to me and that was about 2-3 months and a terrible time cause I told her I would be there for her to talk to her if she had any problems cause I really wanted to get back with her. Then very recently, everything was amazing. She told me that I was showing her more emotion to her and was loving it. She also sent me a letter soon after saying she can't wait to spend the rest of her life with me and many other deep things. Then I talked about commitment and she said she didn't know if she wanted to be with me for the rest of her life. I was a bit angry because I would of thought that she would say an automatic yes. So, I was mad for a couple days and then she was texting me in the middle of the night about her problems then after that she said "I am pretty sure I want to spend the rest of my life with you" and was talking about how she feels so close to me and as one when we make love. Then the week went by and she had been out drinking more than usual and hanging out with guys that I didn't really know. She didn't talk to me much that week and then I found out over the weekend, she cheated on me the week before. I don't even know if there was alcohol involved or not. I was very disappointed cause it happened again. She said she was sorry and that good things come to an end, and that was I was very good to her. Then later I sent her an email 2 days later saying what she is missing out on how I understand her, love her, care for her, and go through anything with her and that I have always been there for her mentally when she needed to get anything off her chest and so on. She wrote me back saying that I was good to her but, whats the point when im never there {meanwhile I would have been back home in 2 weeks for summer} and her co workers were seeing her unhappy. She also said she wanted to be single and see where it takes her and wanted affection from guys. After that, my step-dad sent her something on facebook and she was pissed beyond belief because what he said was true. That she needed help and she just screwed up something so good. Then she texted me I will never be with you again after what your stepdad said. I haven't talked to her since and its been 2 weeks. I can't see it lasting too long since we talked every day, she really doesn't have anyone and everyone is just telling her what she wants to hear, not the truth. What do you think will happen? she is acting as if nothing has happened and being all happy and not even acting herself at all. She is being the complete opposite of how I know her and I am one of the only ones that really know her. . I think its a manic episode and shes running away from the problem cause it never really came to a real close. Shes keeping herself busy and blaming me for her unhappiness which is totally wrong. She does have depression and it may be bipolar

RUN.. run while you still can.. there will be a life of misery with this girl.. i know, i spent many years with a man who had depression, get out while you have this chance, meet someone nice, you are not a councellor or therapist and you shouln't be expected to be one, relationships are about having fun and enjoying life together, you and her sound like hard work, good luck!