Most Helpful Girl
There was obviously trust issues between you two in the first place if you began to pretend to be someone else to see how she would react. She probably feels deceived and ashamed and embarrassed at the whole thing. Relationships don't work if there is no trust as you have found out yourself and so it is for the best that you break up with her. Often cheaters blame and accuse the other person of cheating too as a reaction to be caught themselves. If that is the type of person she is then you are better off without her.
I would also advise that you think about what it is that drove you to take the action that you did. If you didn't have trust in her in the first place, think about what she had been doing before then to make you feel like that. In your next relationship you should try to avoid doing the same thing you did here.