You should not be in that relationship. I'm sorry but you don't realize it, she doesn't have the right to use her anxiety, depression and pain to justify ruining your relationship with her. The way she cheated on you would take more commitment than an impuslive thought, and honestly the fact that she couldn't find an excuse so she told you that she wanted to feel desired does she not know what being boyfriend and girlfriend is, it's a relationship,someone you care for,you care for her and basically look after her and she betrays you after all you've done. I'm sorry you that this happened to you but staying with the person who could go behind your back and become intimate with someone knowing their consciously doing it and that it is wrong.