I know it'd hurt the ones I love, but no, the world wouldn't stop spinning.
If I were to die now, I'd be fine with that. I'm eighteen currently, and being eighteen is a beautiful age. You're not a child anymore, and you're not yet an adult. There's a fine line, and that's eighteen.
If you're thinking about dying, see someone. Please. Keep a journal, keep your mind occupied, do things you enjoy, call a helpline. You seem like you'd be an amazing person from what I can gather, you've just sorta gone off the rails mentality-wise. I'm sure if you apologised to your friends, they'd forgive and forget. At least you have your brother. Talk to him. Tell him your problems. Just try to stay alive, please.