My 18 year old step son has lived with us for just a few months and has told his dad that he is not happy living with us. His plan is to move in with his girlfriend in a few months once they get settled into their new house. My problem is she's living with US. I don't know why I don't like this. Is it because I'm feeling used? Or that we're being taken advantage of? Or that I want my privacy back? What is it that has me so upset with this situation?