I've been dating my girlfriend, Harumi, for half a year now. Her mother, Mio, is a beautiful, hardworking, mature woman with a calm demeanor who has raised her daughter as a single mother. But the truth is, I've been having sex with her mother, without her knowing. Both Mio and I know that this kind of relationship is not good, but whenever we're alone, we just can't help but rub our genitals against each other.