All three

Your brain was on auto-pilot, set to fuck. Your sister's pussy juice, as little as it was; just that heavenly coating as you slid against her, was mingling with your own precum. Something over took you and you took one hand off your cock and tasted it.

Tasted her.

You.

Both of you.

And you loved it.

On the other side you heard your sister whimper.

"Fuck me. Please John." It wasn't just a whimper. There was a desperation to it. It was almost a prayer. "Please..." she said with a whimper...a wish... "I know we...fuck...mmm....we....mmmm.....ohhhhhh....fuck....we.....shou....should.....shouldn't...." she panted as you heard her voice get higher and higher. Your balls felt like they were boiling and you wanted to taste your little tease of a sister's pussy.

"Should...shouldn't.....fucking....should.....SHOULD!" she shouted into the empty house. Except it wasn't empty. You were two inches away from her, separated by your bedroom door. Fuck...why...why was the door closed? Why were you leaning against it? Why was she?

"OH FUCK!" your sister cried in the hallway and you heard her slump, her knees having given our. "FUCK YES!" she cried just a little softer into the empty house. Except....except it wasn't empty. You were right fucking there...

"FUUUUUCK!" she screamed this time. Not a cry, not a plead, but an all out scream of pure, **** fueled, lust as she came. "MMmmmmmfucck!" she screamed again.

And again...

And...