JWS~ Im so sorry this has happened. how horrible. I agree with your friends though, you should stop paying her bills. That is not your responsibility anymore. She chose to hurt you and leave you. Its not helping your situation any by helping her pay those bills. She is taking advantage of you which is not good. I know it sounds harsh but she needs a good dose of reality. If she wants to talk to other guys like that while with you then she needs to find a way to pay for it herself. You are hurting yourself more in the long run by paying her bills because you see these numbers and it gets ur curiosity going.
I think you are making that choice because it is the right thing to do. Your not doing it out of anger. Last time i checked friends didnt pay for other friends bills. Let her see what it is like without you and hopefully that will open her eyes to how good you were to her.
I think once you stop paying her bills you will feel better. You may still think about who she is calling but you wont be able to check which is good. We all have these kinds of days, just keep thinking positive! My thoughts are with you!