My best friend and I have been close buddies for more than 10 years now. Ever since the first year of highschool. Once we reached our 12th and final year of highschool his younger sister had just started her first year in grade 9. I’ve seen her at his house before when i would go over, but thought nothing of it. After she came to highschool, her breasts we’re larger and she always wore a skirt and this just started turning me on. I started flirting with her online and then that led to her sending me n*** pics. Finally the same year at my best friends surprise birthday party we all got drunk and his sister and i somehow ended up outside in an alley-way and we made out, i took her top off, she took my c*** out, started giving me a h******, and then sucked my c*** and that was it we didn’t have s**. We just walked back into the party like nothing happened. Ever since then i’ve been f****** her on the side, even when i had girlfriends and she was in relationships, and nobody has any clue, LIKE NOBODY. We get so spontaneous and risky that sometimes if i’m at his house and he goes downstairs to make some food while me and her are upstairs, she’ll just reach in my pants and pull out my c*** and just start stroking and sucking it and then when we hear him coming back upstairs she just sits right up and acts like nothing happened! And he is SO clueless. i feel bad, like SO bad. but i cant get over the rush that it gives me and the fact that he doesnt have a clue. And this guy loves me to death as a friend. Yet i’m f****** the s*** out of his younger sister.