Until you are emancipated (e.g. until you turn 18; and possibly longer, if you continue to live with them and be supported by them), your parents can control you in this way, including banning you from seeing your boyfriend. Once you are emancipated, they cannot. If you want to understand how and when you can be emancipated, and the consequences of being emancipated (e.g. no more support), speak with a family law attorney.