What can you do when a girl will simply not let you go even after ten years?

I am now happily married. And yet still sometimes I cross my ex on the street and she insists on coming to an encounter in a hotel room. I am really upset by these propositions. After I leave the room I tell her its the last time but she just laughs. I have a wife I love and I am wondering whether this other woman will ever go away. How can I make that happen?