It may be that you have come not to expect loyalty or caring or honesty from her. It may be that you have made up your mind that she is not the person you want to spend the rest of your life with even though you have not yet spoken the words aloud. You do deserve better treatment, and as long as you stay with this girl, you will not have the type of loving relationship that we all search for. She has proven that she is not capable of being true to you. The question is not why are you not angry, the question should be: "How long are you going to endure this type treatment?"