Family Secret

I have 2 siblings, an older brother who is in college and a younger sister in middle school. My brother is your typical football playboy with lots of girlfriends since his highschool days. He was also very touchy with us but being siblings, I didn't think much of it. My sister on the other hand, is a straight A student that the whole family is proud of. She is always top of her class and seems to have a much more interest in books than boys.

So imagine my surprise when I heard moaning of sex in her room. Sex sounds is nothing new in my family as my brother always brought his girlfriend home when he knew my parents were not around but I was not expecting it from my sister room. I just thought that my sister has finally reach that age and maybe started dating a boy without us knowing, or maybe experimenting with a girl like I used to do when I was her age. My surprise turned to shock when I saw my brother leaving her room. He was shocked to see me too and quickly left. I needed to know right away so I walk straight into my sister room and there my sister was, naked, mistaken the sound of her door opening to be my brother came back for another round. My first thought was he r**ed her but my sister assured me he didn't. Apparently she is interested in sex but doesn't interest in any particular guys in her school. So when my brother got touchy with her she responded well and encouraged him for more. They first had sex last year and continued having sex whenever he came back home from college. She made me keep it a secret and not tell our parents. Now I have this gigantic family secret that I can't tell anyone and it's driving me crazy. Hence my confessions