This girl i have known has a bf and says she loves me.

I was wondering if anyone knows psychologically what is wrong with this girl? I know i did something very stupid and I will try to cut this short. I dated a girl for 10 months when her bf was deployed over seas because she told me that he cheated on her a few months before he left, that she did not know if she still wanted to make it work with him. So we started talking. Basically we were together for 10 months as if WE were bf and gf. Also I had a huge crush (one of my biggest) on her since i meet her which was in high school about 11 years ago (we are 26 now).
In this 10 months she told me I was perfect and that she has never been more in love with anyone in her life. Basically she told me that she did not want to break up with him while he was in a war zone because he might be so upset it could get him killed. But also she said she wanted to wait for him to get back home to see if she still had feelings for him because he was acting different. She would always tell me how she didn't like this about him but like that about me. Mostly telling me bad stuff about him. She had also told me very serious things like "i want to have your babys" "if i could i would marry you right now" "i wish i was your gf" "Do you believe in soul mates? because i think you are mine." "you are my soul mate and i love you" but also said she needed to figure out her current relationship? I told her on about 3 diffirent occasions that we should prob just be friends and she would always just about cry, one time she did cry and she said she didn't and COULD not be only friends with me.
She told me that when her bf got back she would not be staying at his family's house anymore because he and she were living with each other already for a year or more (they have been together for a two and a half years as of right now). she said she would keep staying at her parents house without him, also she wanted to do that so she could see me she said. Well the day he got back tell now (a month and a half later) she has been with him 24/7 and spending every night over there. And she still texts me every day saying how much she misses me and loves me that she needs time to figure this all out. Also I saw her car there and she had about 7 stickers on the back of her car before this all happened, on the 3rd night at his house I saw all the stickers were off her car after 2 years of having them on there... which i thought was very weird like she was trying to hide her car.
I asked her if she took her stickers of "because i thought I saw her driving" and she told me "i have not touched them as far as i know they are still on there" so i asked again and she said they were still on her car... which means she was trying to hide something. I then asked her why she would lie about her stickers and lie about saying she was not going to stay over there and she told me she was not lying and she has never once lied to me. And that she was staying over there because she got kicked out of her house... LOL. All the sudden the day that he comes back a year later she is kicked out of her house... right.
I don't understand why someone would do any of this to someone. Also there is a lot more about this girl like her having a lot of narcissistic traits. She was very controlling over who I talked to, she would get very mad and give me "the i cant believe you" squinting eye look when she THOUGHT i was looking at another girl in public. She would ask me who i talked to on many days. She would start arguments about things like when we were at the drive in i looked at the other screen to see what was playing an hour into our movie and she got mad thinking i wanted to check girls out on the other movie. She would sometimes hang up on me even if i said i was watching a movie which had a pretty girl in it, she got mad that a girl asked me a question at work one time and that i laughed at a joke from the girl at work.
She would always call me every morning and ask me to go to sleep on the phone with her every night. She was very clingy and needy. The guy she is with pays for all of her bills and buys her things, like gym pass, phone bills, said he wants to get her implants and gets her nails done every other week, pays for food, Disneyland season pass etc etc.
So my question is why would she get/act so involved with me and want to do things every min of the day with me and spend all of her time with me and if we got into a fight she would always call me 20 min later or come driving back to my house to say she was sorry and beg for me back. But now this guy is back home and she has not even came to see me one time and she has not even called once in a month and a half but still sends me text messages telling me and i quote word for word "i miss you so bad it hurts" "i feel so lonely without you my heart feels empty" "all i think about all day is you, i wake up and you are the first thing i think about and when i go to bed you are the last thing i think about before i am asleep" i stopped texting her telling her she was a liar and i am done talking to her if she wants to lie to everyone and be with someone else and basically that she was bs'ing me and she used me so I was not going to contact her anymore.
She called me mean and said "how could you not talk to me anymore all i have been is honest with you" "i am so sorry this hurts i am hurt to, i hope you know how much i truly love you with everything in me." many message saying "PLEASE talk to me, I am begging you!" "Ill do anything! please tell me what you want me to do!!!!!" "PLEASE, you mean way to much to me" "I don't even get along with him!!!" "You are the one i should be with, you are my soul mate" "I love you, you are my best friend and my soul mate" I told her to lose my number and that I don't want to talk to her ever again for what she has done in betraying my trust and she said "I would never get rid of your number i love you" "how could you be so damn evil and mean to me, I am so stupid for trying to keep you in my life are not I" "All i have been doing is trying to get you back and you wont even give me the chance to be with you" Even though i am pretty much over her and know she wants her bf now that he is back, I am okay with it that she wants that and is making that decision because i cant force her to love me and want to be with me, also I cant trust a liar and this has been a learning experience. I just wanna know what is wrong with this girl and why she did/is doing this, from a psychological point of view...