Tricky situation. If you're not happy and comfortable to stay with her, then tell her how you feel, see if she's willing to make a change for you. If you don't accept her terms, then perhaps you should walk away. I was in a similar situation as your girlfriend, I was seeing a girl and we had a relationship while I was (and still am) having sex with other women on the side because she wasn't good enough and I needed more than one girl to satisfy me, but I didn't tell her about it because I knew she wouldn't approve. Ultimately I had to let her go because I didn't want or need her anymore, I was getting what I needed from the other girls and she was against the idea of an open relationship and I'm much better off without her, she didn't understand my needs. Most people aren't comfortable with the idea of an open relationship because they need to feel like they own the other person for some odd reason. On the one hand, I think it's very selfish to demand from your partner that they only have sex with you (because it's impossible for any person to be satisfied by just one man or woman), but on the other hand you need to do what is best for you. Are you willing to stay in this relationship, do the benefits outweigh the problems? It's a question for you to think about. You're allowed to have your own needs and you're allowed to make demands but you can't expect to always get what you want.