He's not some "guy". He's your brother. You've also referred yourself as a nymphomaniac. You've posted nude photos of yourself online.. and you're a minor. Your whole family have been made aware of this and are greatly concerned. I suspect because of this, you've made your brother uncomfortable.. so the sight of you in a bra is now a trigger for him. He doesn't want to see his sister in a sexual way.

I'm surprised he's still walking into your room.