How do i get out of the "brother" stage with this girl?

So Im a 14 year old girl and I have like the same thing happening with me just the other way around. This guy in my class is my best friend and I could really tell he liked me and at first I liked him back. And eventually he asked me out. I was so excited at first and then after 2 weeks I broke up with him. I did this because he got way too clingy and started showing off that we were together. So if I were you I would really impress her and show that you can comfort her when shes depressed about this guy. Spend time with her and you will eventually win her over. Trust me a girl likes to see a guy show emotion and also be tough at the same time. And when you do get her just make sure you don't get cocky because thats a total turn off. Lucky girl ;)