You are missing the point... Even if she is in fact completely aware of the repercussions of her behavior, she is still doing the best she can. It's all she knows how to be. The reasoning is not important. Would it make you feel better is she had an abusive father who molested her constantly and now she thinks all men are scum?
As far as my analogy and cheating... I'm willing to bet that there were plenty of situations prior that where she did something that you didn't particularly like. She was late when she knew you were in a hurry. Perhaps she was rude to you friend. Maybe you asked her to do something and she flaked out. If you didn't stand up for yourself in those situations, then you have conditioned her to mistreat you. Until she started cheating.