I feel like a baby

I have been journaling about my brother for a while. And about how he's a pot head and stuff. This has been eating at me all week. Last Thursday night we were texting and he said we had to leave like ten minutes earlier to school and I asked why an he was going to smoke before school. In October he told me he would never do that, go to schoool high. Funny how fast people change. Anyway, I started yelling at him. He had just started varsity basketball and I know if he got caught he would so be fucked but he's to dumb to realize that. So basicly I brought up his girlfriend and he flipped. He toldme to " keep my fucking mouth shut." and I said I would do what I wanted and that's when he said that If I told anyone that he " would punch me In The fuckin face. I don't give a shit if your a girl. Your my sister and if you get me in troble you'll regret it I promise you. So watch you back"

That's about when I started crying. Thats the exact text. Now what am I to do? He's definitly got a problem and he doesn't care i'm his sister obvously. I didn't realize he could be such an ass. And today at school I heard he cheated on his gifriend. He says he didn't but really I don't believe him. I'm going crazy. Do I tell my parents and try to get him help or something? I don't know anyone anymore.