she's deliberately lying to you and admits the act so that you will break up with her. face it, she might just be giving you the reasons to break up with her coz she cannot do it herself.

lay the cards on the table and just confront her with it. just let it out of your system and be frank with her.

it is true that you have to trust her and give her the benefit of the doubt that she is telling the truth, but man, you must also be honest with her about how thing are affecting you.

good luck!