How should I fight for her?

My ex broke up with me and I am certain it is because for the entire year and a half years that we have been dating, her ex boyfriend has been trying to get her back. We grew apart and when she went home, she started talking to her ex again. When she got back, she said that she wanted to take a break. Two weeks later we started sleeping together again, but only once or twice a week. Over the entire break up she still claims to love me, talks about moving home with me after graduation, and she still calls me everyday, but things are different now. Before we spent every night together. We just started sleeping over again within the past week.
The tricky part is that she about a month ago, she was really keeping her distance so I put a note in my phone that said "I hate her so much right now, I gave her so much, she doesn't deserve me." The next day she made a flight home and called to tell her old boyfriend she was coming home. In the past week she has asked if she wanted to get back together what would she have to do, but she still went home. She left yesterday and she has only been calling me in the morning.
It is worth noting that the old boyfriend cheated on her before, is 2000 miles away, less handsome (she says), shorter, less athletic, has no job and is not in school. Then there is me, tall, handsome, athletic, romantic, a med student, but less fun. After talking to mutual friends, I estimate she thinks of me as the perfect guy except there is a certain spark that I am missing. Too good to let go.
I didn't take her call this morning because I felt like she was calling me to get the check in out the way. I could call and confront her and say I know you have been talking to your ex. I could continue to be romantic like nothing is wrong and hope that her conscience will keep her from sleeping with him. I usually send her texts about how I miss her and things I'd like to do to her throughout the day. I could continue to ignore her calls. Lots of people have told me to move on and that I could do better. I don't want to. I love her. The thing is last night my love got cut in half because she isn't cheating on me because we aren't together technically at the moment but if I think she had sex with this guy I won't love her the same way anymore. How should I handle this?

If she calls back, ask her what's going on and be upfront about it. If she doesn't call back (which I think she will), you should call her and talk to her and see what it is that both of you want. Lay it out because you can't hold onto something that doesn't wanna be held onto. You shouldn't pretend like nothing's wrong because something is wrong! You should always voice how you feel because maybe she doesn't understand exactly how it makes you feel because she's too caught up in her own feelings but if there really is love for you, she wouldn't want to hurt you. My guy and I had a talk one time that no matter what, we'd talk about it and work thru it and communication is part of what is the foundation of a relationship, along with trust--this situation is really challenging both of those things. The best of luck to you..