We appreciate your efforts to ask this question on the forum.
The answer to your question is "NO". Your orientation (Heterosexual or Homosexual) cannot be decide by certain acts or exposures with anyone. Sexual orientation is natural phenomenon and you get sense of your sexuality at the age of 13 or 14. However, I would request you to have conversation with your brother regarding the same and if he's under 18 years seek a help from professional counselor on the immediate basis.
You can also call at Humsafar Trust on 022 - 26673800 where our counselor will help you with more information.