Why does my brother hate me so much?

I'm 13 and my brother is 15. Even though I just act casual and don't talk to him much he says I'm a punk because of the school I go to (we go to diff schools) and that everyone is a drama queen or king even though I don't talk to him all that much , let alone about anything at my school. So one day he started getting mad at me over a computer and who's turn it was so he punched me in the face and we got in a fight. After I decided to just walk away he threatened to beat my *** and pulled out a pocket knife and told me to get out of his room. As I was walking away he told me to go kill myself. So, since at the time I was depressed I tried. I took a bottle of zyrtec and read that it could cause liver damage, coma, or death. So when everyone was asleep I took 25 of the zyrtec then after an hour I fell asleep. The next day I woke up and nothing had happened. So two weeks later my parents and my brother found out and I had to go to a counsiler. Afterwards he still acted the same as before and when he told me to kill myself again I told him I tried to because of him and them he told me that I was being a whiney little ***** and that it wasn't because of him. So why does my brother hate me so much?