Doing this in itself will show him you're not a child. Then try talking to him as an adult. Let him know that you want to work together and make this work. Share with him how you think you can help him and you think he can help you. Always remind yourself that he's only trying to protect you - especially given the circumstances.
All parents make mistakes, especially big brothers.
Let him make his mistakes, but work with him, not against him. While you will always be his little sister, you're certainly not a child. I walked alone, sat alone and did my homework next to the ever-silent telephone in hopes that someone would call for help with an assignment. This was my world and I felt only numbness when I passed through the cafeteria and saw the last remnants of tinsel hanging from the ceiling after the prom, after yet another group of s pushed past me and ignored my futile and fleeting smile. I'm now finishing my first year of college, and I've learned to be actively happy.