can a 17 and a half year old move out with her boyfriend without the law stopping her

Unless you have been legally emancipated by Court Order, you are a minor and under the control of a parent or guardian until 18.  If you are away from home without a parents' permission or consent, you can be considered a runaway. Until you are 18, your parents are still suppose to be providing for your support and maintenance.  While it may not seem so, you will be 18 soon enough, and then able to make your own choices and mistakes, and be financially responsible for yourself.  At 17 1/2, you should be concentrating on enjoying your senior year and graduation.