Sheepytoons Offline

I want to ask a question. My little brother is eleven years old, two years younger than me. He used to be a amazing brother and I liked him a lot. He recently joined secondary, middle school and started being cocky and horrid. He always makes jokes about me, saying I'm a loner and have no friends, this , of course isn't true. He always blackmails me and never lets me join in. He comes into my room when I'm relaxing. When I shove him and tell him to go away/Knock on my door first, he comes up with the same crap statement. He says I've bullied him his whole life and that I'm a horrible person. I really want to beat him up. But if a lay a finger on him, mum will be all defensive and say he's stressed out. Well so am I. I'm sick of it and am a very sensitive person, he is getting away with giving me crap and when I do something about it, I get the blame. He is blackmailing me into trouble, and kind of bullying me. I can't tell my mum because she doesn't get it. I need help and advice, before I loose my cool and knock him out. Cheers...