i need advice for my relationship/breakup ???

i need some serious advice on how to win a woman back that i recently had a young child with . My scenario is that we had our daughter on christmas and every since cristmas she has acted as if we werent even together. Everyday i would come home and would find the house a mess and i would go to bed worrying if she was going to be there tommorow when i come home. So i eventually became tired of it and didnt felt that she loved me so i did the wrong thing of sleeping with another girl. which turns out she could be pregnant by me and a couple of weeks after the incident i felt that i couldnt hold it in and had to break the news to her. When i told her she immediately burste into tears and i explained why i did it. i also told her to promise me that she would never leave me and take the child away from me. Not to mention her pushing me away all this time she also has a friend that comes over all the time that has a expensive living style which my ex adores. So everytime shes over she gets all these ideas in her head about us moving to where her friend and her friends boy frind live and i tell her to be patient. Reason being is because moneys tight right now and so forth. She treats me like total shit every time shes over here. If i ask her something she ignores the question or gives me a big attitude so i say forget it and go on about my business. Then at the end of the night she tries to be all lovey duvy but by then im so hurt from this so i ignore her. So recently we recieved our income taxes and as soon as she recieved it she came home next day packed all of the babies clothes crib etc and left. She told me its over and left to go live at her friends 2 bd rm apt with her and her boyfriend with my kid also. Its so hard to be without my kid i need her here next to me everyday. So two days after she left me she text messages me and gives me her new # and said call if you wana know about your kid . So i tried to call and she said stop calling were are done its over with. I tried to explain to her that we need to be together to raise our daughter because we both came up in broken homes and i dont want her to go through with that. But she insited on saying leave me alone we are done forever.So i texted back fine i will leave you alone. Then she texted again with a message reading we will never be together ever, as if she was trying to rub it in my face.She also stated when she was moving out that she loved me but couldnt do this any more. She also im assuming called me before she recieved her new number private and hung up on me maybe to hear my voice or something. So i need advice on how to win a woman back that i have been with for two years through thick and thin times and who has my daughter??????????shes 19 by the way and im 20

maybe its post pardum depression...how old is she