Used need help

First I know that it is over but how can I want the person back in my life???

I met this young women bye accident. We worked with each other and one day her ride couldn't take her home so I volunteered. We ended spending a lot of time together until one day she said come here I have to tell you something and she kissed me. She didn't know this but I actually fell head over heels for her when I first saw her taking her ID picture at work. Needless to say I knew she had a child and I didn't know if I wanted to date someone with a kid.

We started to hang out and eventually she tried to sleep with me, which I said no because I wanted just more then sex. After about 2 months we started dating and became inseparable. Unfortunately, I didn't know that during this time she had a bf, which came over every weekend. When I found out I asked her its either him or me and she chose me. Well because of her lies to her family they kicked her out of the house. One day she shows up with her and her son and no place to live. Instead of running for the hills I take her in and she stays with me until she finds somewhere permanent to stay. Also, during this time I heard that she slept with someone I know during the first week we dated. She begged for forgiveness and I said ok lets start over. The relationship continued but I never took her to my parents because of the jealousy and possessiveness she showed. Finally after our one year anniversary I broke up with her because I couldn't take it anymore. She cried and begged and after a month I took her back.

The day we got back together she asked me to go to a b-day party of a friend of hers. I said I wasn't feeling good but go have fun. Well when she came home that night she told me that she was the only single girl there and that this dork was hitting on her. I laughed it off. Well I find out on Jan 1st that, that dork is the person she cheated on me with. She carried a relationship with him for three months while she came back to me and told me she loved me. I baby sat her son overnight while she cheated on me. I asked can I go when she went out but she always said it was girl's night out. When she told me what happened I was irate but she cried and begged me back. I said ok we will work through this and I love you. Then she dropped the bomb. She said she was pregnant and she had an abortion the day before. She said she knew it was not my baby. I said how and she said she had unprotected sex with him, because he liked it that way. Of course I was heart broken because we were talking on Christmas about getting married and kids. I still take her back and actually I called in the next day to take care of her.

That night when I dropped her off I order 4 dozen roses and tell her that we will work this out. The next day she calls me and tells me it's over and that she hates me. She then goes to my friends house and tells them I am a psycho and that I am fat and she didn't like to have sex with me. The next day she calls me and begs me back and of course I take her back. The week went by very well and we were like we were when we first started dating. That Sunday we went to the mall and looked at wedding rings and I called my parents and told them about her and she called her parents and told them we were getting married. Then he called that Monday and wanted her back. She called me and told me about this but to not to worry she loves me. We actually were going to sign a lease together that Tuesday but the apartment was not ready so we didn't. The last night we were together we made love and she looked at me like she never did before. She also said I love you and this will work.

Well the next day she calls me and dumps me and says she wants him. She tells me that the sex with him is great, he makes more money than me, I can never see her son again (He calls me daddy) and he gives all that she wants. She said she had to beg me for stuff. I just took her in, gave her a car, a phone, clothes, potty trained her son, support and all the love she needed. She later calls me to say that she heard that I was seeing a therapist and that I was crazy and she doesn't want to be with me. She calls me the next day and then tells me that she might want to work things out but that it will be hard and I said ok. Well she then calls me the next day and tells me that she hates me again. I try one last time and wrote her a letter from my heart. My friend actually cried when she read this. She calls me and tells me that she got my letter and that it meant nothing to her. I am devastated now. I have lost 30 lbs since Jan 1st and can not get her off my mind. It is ruining my life. I can't function or sleep!!!! Please help!!!! Why do I love her so much!!!