Most Helpful Guy
Did you promise her that you would be monogamous, or did you do anything that would make her think that you have a monogamous relationship? If so, you have two options that preserve your honor:
1. Promise yourself to honor your commitment. Discuss the sexual matters with your girlfriend. Promise yourself that you will act like the man that you want to be.
2. Tell your girlfriend that you are unhappy and you want out of your commitment. AFTER that conversation, you are free to pursue other relationships.