I am proud of you for telling your mom. If your relationship with your brother was different - maybe YOU could have handled it - but you indicated that it was not like that - so I believe you did what was best and what you had to do. Good for you. It will protect him in the long run. "Telling" is not popular - it is a hard thing to do and may draw criticism - but in this cae - it was protecting your brother. You are a good sister was braving this controversy. If you were my daughter, I would be very thankful and proud of you.