Older sister is taking over my life?

im 15 and home schooled my older sister has known something about me for about 5 years now shes 18 and still living with me and my mom. when it started she started making me clean for her and if i didnt she said she would tell all my friends. and up to now its getting worse for example the other day i was at a friends and my mom had to go to a wedding but i was very tired so i told my mom no thx im pretty tired so i was going to stay at my friends for a couple hours till my mom got back and i get a call from my sister 20 minuets late or so and she says were coming to pick u up to go to the wedding but i told her mom said its ok cause im tired she said no your going and it was on speaker so my friends could listen and i just kept saying no and she started calling me names ik not to yell at her cause if i do shes going to cause problems so i ended up going cuz shes a brat. idk what to do i end wanting to kill myself becaus ei cant live with her we probably have fought a thousend times and every time she wins just because of the thing she knows about me im scared she might tell me family and friends and theyll all hate me or stop talking to me the thing she knows about me is completley harmless but its very imberrasing to me. shes the type of person who gets mad all the time when she doesnt get her way. she talks about me not giving her respect. um hello! u took over my life for the past 5 years and u dont even realize that. she doesnt respect my mom she yells at her if my mom trys to stop her from yelling at me. and this one time a year ago my sister said she wants to do my hair and i told her no its fine im just putting it up and she threatend me so i sat down and i was trying to pull away and she pinched my arm and wouldnt let go and started yelling at me so i screamed and she socked me in the eye and i got a black eye. no one knows about this my mom just thinks she slapped me.i can never explain to my sister everything she does but she just yells. i hate her to much now i cant stand it what should i do?