It was a black ass that was always in front of me... I live with my girlfriend and her sister. My sister is a gal and doesn't wear skirts at home, she always wears thongs. I wonder if she doesn't think of me as a man. I couldn't keep my sanity as my sister walked around the house with her black ass sticking out... I got a full erection, pushed her thong aside and inserted myself from behind. I lost my mind and forgot to put on a condom and kept moving my hips until I came inside her.