I got a hard-on with my sister’s friend

Your sister’s best friend slept over at her house. Her brother, who is a pervert and spends all his time watching his sister’s friend wearing her shorts glued to her body, showing the whole shape of her body with small breasts! She knows well that he keeps staring at her. In the morning, her sister’s friend went to the bathroom to sanitize herself. The careless brother, on the other hand, went to jerk off in the same bathroom as his friend. And there she was surprised at what she saw!