OMG! Whats going on?

I'm having a bit of a situation. The story is...I met this girl at school. I got her number and we started texting. Pretty soon we started to call each other and talk all night. Then I found out that she has a boyfriend. So we keep talking and flirting and then we started to hang out. She eventually tells me that she likes me and that she might break up with her boyfriend. I didn't believe her at first but then they started to fight a lot. They didn't talk for a week and the two of us grew even closer than before. Then out of nowhere, without even telling me, they get back together and are the happiest couple ever. Her boyfriend then calls me and starts talking mess and wanting to fight. Her and I got into an argument over it and we were never the same. After a few weeks of me being heart broken, she starts talking to me again like nothing ever happened. And after a few more days, she won't talk to me. Whats going on? And how do I ask her how she feels without pushing her away?