Why am I having sexual dreams about men I don't know and can't remember the dream?

My boyfriend has told me that I am moaning and acting like I'm having sex while I'm asleep. I have touched him and started rubbing on him and all. The thing is I don't remember any of it! Also, I am saying different men's names, most of whom I have never heard of!!! This is very very frustrating for he and I. It's also very hurtful for me to know that I am doing this and he is having to listen to it. Please any advice that you could give would be helpful!