It's obvious to me that she cheated on him, and she doesn't know how to get out of it. She is trapped in her life of sin, and she sees no way out of the situation. The voice in her head was Satan whispering to her, and she listened. She now realizes the mistake she made, but she feels it's too late. The other girl has yet to come into the situation, and she hates the thought of him with another woman. She thinks that there is no way he can trust her again, and so he would be better off with someone else.