Family Advice. Sister in bad relationship.?

My little sister is 15. she has been going out with this boy who is also 15. From the very start i hated him. he Controls her and he also used to hit her until i told my parents. he also left me with a bruised arm. he got a kicking one night about a month ago and i was there. But the problem is that he got into a fight with my Friend the last day and i was also there. My friend said hello to my sister and he hit my friend leaving him with a nasty cut on his head. He tells my sister what to do and i never see her. but one night i asked her to go to the fair with me and me and him got into a fight. I am blamed for everything happening in their relationship. His family are not a good family either. After the fight with my friend my sister wasn't speaking to him for a while and then she started speaking to him again. I gave her advice but she says he wont listen. He cannot accept the fact that my sister has to spend time with her family and even at school she has lost all her friends because of him. I am really scared for her safety and my safety as well. She do sent understand that he is ruining her life because she hates school and has no friends. I don't know what to do. I don't want to fall out with her and im only looking out for her. Can anyone give me advice on this situation. I am only 17 but i am worried. Please help.Family Advice. Sister in bad relationship.?
if you poke your nose in too much, she will become rebellious, so go gently with her she'll learn the hard wayFamily Advice. Sister in bad relationship.?
you need to talk to your parents about this. she should not be allowed to see someone like that. she will probably be pissed at first but in time she'll realize that you are only trying to help her. change your phone number and im sure, cause everyone has one, she has a cell phone. change that number also
You definately need to go to your parents about this. It sounds like this boy grew up in an abusive household and that's where he is learning this behavior. Your sister needs to break off complete contact with him. Inform the school that she attends that this boy is controling and violent twards her. If this doesn't work, involve the police and a restraining order.
Let her figure it out .... she wants to get out of it without losing face, but can't see a way. An opportunity will present itself soon.
Your sister will only learn from her own mistakes, the best thing you can do is to be there to support her when it all falls apart, she will realise in her own time what a waste of space he is.