Damn. Sounds like she is a right bitch. Your conclusion, I'm afraid, is probably the right one. I had a mate who cheated on her man, and even though she told him, they only lasted a few more days.
She should really tell you the truth, because if she really does care about you, then she would. Saying 'I don't want to hurt you' is just a cheap way of trying to get out of what she's done.
Obviously though, if she hasn't cheated, you have to give her the benefit of the doubt. There is always a (very slight) possibility that she does think if it's best you're not with each other.
Look on the bright side though, at least she hasn't led you on or messed with you even more