She is saying he underestimates her and she doesnt need him. She could have another guy just like him at any time. He is on his way now. "You must not know about me" meaning "I'm sure you don't know something about me." is correct(:

Does "You must not know about me" mean "I'm sure you don't know something about me." Yes, or "You obviously haven't heard of me (even though most people have)" or "I demand you not to find out about me."? No, although in a different context it could mean that. She is saying "You don't know about me or you would realize you are not special and the world is full of men like you. I could have my pick of them." She is also saying that a lot of people do know that she could easily get another man.