a few years ago i was spending the night at my girlfriends..as usual right before we went to bed we fucked...it was fine..she came gloriously and fell asleep...but i wasnt satisfied...i went to the bathroom and i saw her sister walk by in just her panties..she looked back at me and i couldnt help but follow her...we never spoke..we knew we had to be quiet...i took her in her room..slowly brought her panties down...and pentetrated her..not hard...remember we had to be quiet...i could see it in her eyes as it slid in slowly stretching out her pussy...inch by inch...i fucked her for hours...i mean hours..slowly..what made it feel so good was knowing my gf was in the other room sleeping...and right when i was about to cum..i pulled out...i grabbed her by her hair with my left hand and opened her jaw with my right...and i came in her mouth...and she loved it..she rubbed my cock over her face...we didnt cuddle..we didnt lay there and we sure as hell didnt talk about it..i walked out...and fell asleep next to my gf..and we never spoke of it again.