@Marbles,
Everyone's family is grating or annoying or even makes us feel bad about ourselves on occasion. Have these people been there for you when you need them. Did they house, cloth and feed you? Pay for your education, sports, proms cars, braces and doctors?
If so, it's pretty selfish on your part. For all you know they find you grating, annoying and depressing. Someday, when you are older your divorce from your family may come back as guilt.
You are 18, get a job, move out. Most 18 y/o only see their family on mother's or Father's Day and Christmas anyway. Is three days a year too much for you?