Girlfriend wants do to it with other people and stay with me. What do I do?

My girlfriend and I had a conversation. She said that she wanted to have sex with other people but stay with me. I was shocked to even hear that come out of her mouth... She wants to stay with me forever and I want to stay with her forever. But she still wants to explore but wants to keep me... What do I do I'm really sad and scared. Please help?