I remember watching porn on my computer with my pants down and my sister walking in. I had forgotten to lock my bedroom door and she caught me watching this girl sucking this guys dick with my hand on my dick. "Oh wait till I tell Mom and Dad about this" she said as she looked on. My parents were hardline Catholics an strict about sexual things. There I was 15 years old, yanking my pants up over my underwear, still half way down my thighs, desperately trying to turn off my computer right in front of my 18 year old sister. Totally embarrassed and scared shitless about my parents knowing, I began pleading with my sister, Told her I would do anything to keep her quiet. Anything?? she asked me with a big grin on her face. "Well you can start by showing me your dick" I was stunned about my own sister asking me something like that, but on the other hand I knew my sister was always hot for sex. She had been trying to see me naked since I was 10 years all and finally had me with my back against the wall. I was still hard when she locked the door and even harder when she told me to get undressed. Sat on the edge of my bed and gave me a mind blowing blow jobs with her hand copping my tight balls. Took her less than a minute to make me cum and swallowed it all. "What else did you see on your computer" as I stood there at a loss for words. "I hope it's pussy eating because tomorrow your having lunch on mine" I learned all about oral sex with her every time my parents weren't home. It went on for the next two years and then stopped when she found a boyfriend, but at least she knew how to keep a secret. We never talk about, but I'm sure we still have lust for each other.