I am her younger brother and it gets me furious when it happens.

Well that must be awkward for u... You can't be mad about her having sex but you can tell her that she needs to be more considering in that case be more quiet... Ask her how should would feel if she would be in your shoes

Hmm well that's sounds like a great idea. I just have this protection issue over my family. I litereally go from 1 to 10 when this happens and I don't say anything because it won't come out the right way.

How old are you and she? How old is the boy? Where are your parents in this?

My Lil brother has the same protection issue and it just causes me to keep stuff from him... If u guys have a more relaxed healthy brother sister relationship she will come and ask u for help if she really needs it sweetheart :)