What to do in my relationship ? Lot of fighting and trust issue
I have been out with my GF for almost a year, we are living in different cities not very far away so we use to meet on weekends when our offices are off. She had a guy at her workplace, who she always tell me is just a good friend. This was when we were not in romantic relationship. When we started our serious relationship She told everyone of her friend except this guy. One day She was complaining so much to me that I don't care about her much but this guy took so much care of her and all. One thing led to another and I got to know She didn't told him about our relationship, when I asked why She told me that he was her boyfriend before me. I was shocked and stopped talking to her. After a while she came to me a apologized and promised me that She will tell him everything about us and She also tell me that they are just friends now. I was ok with that and forgot all those things and one day I told my mother about her and on that very day that guy said her that I'm just screwing with her and will dump her one day, I was hurt that day but again she came with all her apologies and once again we were good. During our relationship She always used to lectured me that trust is a two way path and used get angry with me when we use to go to some malls etc(We generally use to spend our time together at some public place) complaining that I'm more interested in other girls and betraying her etc.
Then after 1-2 months due to some reason my GF gave me password of her email-id. Although it was inappropriate but I saw their chat history and start reading it for the longest night of my life. When I was done reading I came to know that they had physical relationship even after She started relationship with me, they use to go out every now and then which I thought is just a dinner or lunch but use to be something else.
Even that guy use to ask her what she is doing, fooling around with him and had promised me for long term relationship even marriage, for that she said that she love both of us.
When I read her chat history at that time he had already moved to some other study in a new company, that time she told me that his chapter is closed now and she won't call him again (Till that time I didn't knew about these two). Next day we met and I told her that I know about their relationship, She cried a lot and gave a lamest excuse of all her deed that She never realized that one has to be loyal in a relation( This girl can talk for hours over loyalty). I was really hurt and stopped picking her call, She use to cry a lot whenever I pick her call up, and I use to feel bad about her because I'm causing too much pain to her. During all these I told my mom how She betrayed me.
Well after 2 months of crying and fighting we again started seeing each other, but now really don't trust her and whenever I saw a girl cheating some guy in a movie or TV serial it reminds me of her and now a days we are fighting a lot also which is almost every day.
I tried to break things up with her so many times but couldn't able to do it. She always said that she can't think getting married to someone else but never talked to her parents( Thank god) because her astrologer had told her that if she tried to tie knot with someone before Arpil-May 2013 than things will end with that guy.
So please help me out here because every time I break up with her each time I ended up making even bigger promise to her about our future but I'm sure I can't trust her for my entire life. What should I do?