I´m 20 yo and live with my mother and my brother. I always had mixed feeling towards my brother. I always tried to hide from myself that I liked him more than a brother. He attracts me and I masturbated imagining being fucked by him, but I never tried to show it or tell it to anyone. A few months ago things changed. My mother's boyfriend left her suddenly and I didn't quite understood why. They seem to be fine and their relationship what good. I asked my mother why he left but she didn't answer. Weeks later I meet my mother's ex in the supermarket and I asked him what happen and he told me he saw my brother fucking my mother one day when he came home earlier from work. That made a big mess in my head, I always felt something strange between them but never suspected it could be this. During days I didn't know where to put this information in my head because in some way it excited me and made feel really wet. I masturbated several times imagining my brother fucking my mother. Finally I got the courage and talk about it with my brother, not only about him and our mother but also about my desire to have sex with him. Well, this made me loose my inhibitions, if he can fuck mom he sure can also fuck his sister. By the way, our mother still doesn't know we share the same guy.