Love trouble

Last Thusday, after a dancing course, my girlfriend already found some messages from my ex-girlfriend in my cell phone. The messages proved that I still keep contact with my ex-girl while I promised not to contact with her anymore. I don't want to be so serious, I love soft skills, I mean I still want to make friend with that girl. But my girl doesn't want it at all. We had an honour chat with each other, then we agreed that I will limit meeting occasion with the ex-one and if I have to, I'll notice my girl abt the date. I thought that was ok until she asked me why I cheated her then I said that I think she react so serious and I don't want she's like that. I said if she doesnt believe, I can make an appointment for them to talk with each other to make it clear (now I can see how stupid I was) but she denied and said if she come to that apointment, she will say something bad with the other girl. Then she said she doesn't like the way I think abt her. Then we said goodnight.
The next day she come to the capital for her job's training until now. I tried to contact with her but I always failed until yesterday we just said with each others 2 or 3 sentences then we hang up. I could feel the cold in her voice and I'm so self-respect that I can not keep going that call.
I love her and we'r planning to get married next year but sometimes I wonder if we can live with eachothers for the whole life in peaceful. We have a lots of problems, I'm very greedy while she's just like a geek. I have to leave now. I'll continue this subject if I have a chance.