I understand that I can't and shouldn't have sex with my girlfriend' sister who seduces me with her big tits and no bra while grinning like a little devil... but the urge that I just can't control is making my life crazy! There is no way I can win against such an attractive woman who appeals to me for sex! I've had it up to my sleeve, and I'm going to fuck her every day without my girlfriend knowing about it!