How can i tell my mum i was ually abused?

ok....um....i dont know how to start my name is alisha im 15years old i am suffering with anorexia nervosa but im in recovery thats not all my brother ually abused me from i think about 8/9 years old till i was about 11/12 my brother would make me look at naked women and touch me or make me touch myself he tried to have with me many times but luckily for me didnt know how......but it didn't stop him trying.At the time he would call my knuckles(like of sonic)....,,i know this is gross but i need to let this out....(sigh) on a occasion in his room he tried to make me rub myself with my fingers i didn't want to honest! i told him it hurts so he made me use my fist.....he told me it was my own fault and he said my mum would hate me and shed get me taken away he also told me brothers and sisters always do it its normal.....i believed him....but not any more.....anyway the thing is i dont want to tell my mum because im afraid she wont believe me or love me.Me and my sister was having an argument she kept on nagging at me asking why im always moody and angry and i told her well actually screamed it at her......she didnt believe me she said i was lying.....she said that our brothet is not like that.....i didnt want her telling mum and also my brother has tried to commit suicide before and im scared if i tell it might trigger it hes better now but im just scared and that would be another thing my family could blame me for......my brother is 18 now he still visits but is moving in soon he has nowhere else to go but i know he wouldn't do it now he hasn't in a couple of years because i threaded to tell i ran downstairs crying shouting im telling mum! over and over he then begged and said hed never hurt me like that again and he didnt but that doesn't make it ok......i do love my brother.....im already hurting my family with my illness.....help me please kind people what should i do??? xxx