Talk to a parent, teacher, school counselor, other trusted person, or even a hotline. Talk to someone. If a family member or friend of the family is assaulting you, it is not your responsibility to protect the family or to hold the family together. You have done nothing wrong. The person assaulting you is responsible for their own actions not you.
Sexual assault is more about power and control than sex.
You can regain that power and control over your life. Double date or go out in groups. Don t get drunk or high. Never arrange to meet internet friends or acquaintances without the knowledge of a parent or guardian. Adults are not always right.