It’s not healthy keeping your emotions bottled up inside you. Especially since you write you’re afraid that you too will go off the derech. If your brother is a bad influence keep your distance. Be polite but cool. Don’t try being the one bringing him back. He needs somebody who’s experienced in this field. Definitely not a HS(?) girl who’s pretty confused herself. Are you sure there’s absolutely NO-ONE you can talk to?
B’hatzlacha!