She is never going to be monogamous so I would advice against a DADT. You need to keep the communication open for several reasons, like your physical safety. A DADT would spare your feelings but it is in your own interest to not delude yourself about the nature of the relationship you have. Read up on ethical nonmonogamy. People have different resources they like. More Than Two is a popular one, The Jealousy Workbook is another. Individual therapy is often useful. You might need someone who is not your partner to vent to, especially since she is unable to be that person for you. Getting angry when you tell her how you feel about this is a big red flag. It says a lot about her lack of empathy and even commitment to you, and based on personal experience I would seriously question the potential for an equal partnership in this case.