"Ok I dare you"
She stood up and headed for the study. Holy shit. I thought no way she was going to go through with it. Probably she just decided to use the bathroom. I waited expecting her to return after a few minutes. But as the wait dragged on and she didn't return I got a intense nervous excited feeling in my gut. I quietly made my way towards the study.
As I passed the bathroom I glanced inside and saw no sign of her. I approached the study there was my dad sitting in his chair, his back towards the door and there was my gf naked kneeling in front of him stroking his cock. She looked over at me, smiled sweetly, then looked at my dad and lowered her head towards his cock, I watched as she took him in her mouth. He moaned and my cock sprang to attention. She bobbed her head up and down his cock taking it all the way in. She continued to take him into her mouth and throat. I watched as she pulled her mouth off and used her tongue to dance around his crown as she played with my fathers balls. Her hands moved up and down his shaft as she ran her tongue down the length of his cock stopping to lick and suck his balls then back up again so she  could suck his cock some more.
After a few minutes she pulled her mouth off of him, she stood and while facing me she moved forward over his lap and I watched as she reached down and took a hold of his cock guiding it towards her shaved pussy playfully putting the tip at her entrance.
"Shouldn't I wear a condom?" My father asked.
"Probably, I'm not on the pill"  she replied. Looking at me and bit her lip as she slowly lowered her pussy down onto my father's cock, letting out a moan as his cock buried itself in her cheating cunt. She began to ride slowly up and down up and down. I watched, transfixed as my own fathers cock slid in and out of my girlfriends unprotected pussy.
"Oh daddy.." she moaned.
His hands were busy fondling her tits as she began to pick up the pace, faster and faster she bounced on his cock. She started to kiss him, their tongues clashing as she rode his cock and he continued to play with her tits.
They both stopped making out as the fucking became more intense.  My dad groaned and she was moaning like crazy and she looked at me as she fucked him.
"Do you like my pussy?" She asked.
"Oh my god yes." He moaned
"Fuck me daddy" she moaned as my Dad sucked on her tits while lifting her ass up and down on his cock.
"Your cock feels so good daddy." she pulled him to her. Kissing him with a hunger that I've never seen from her before It drove me crazy watching her make out with him while bouncing up and down on his hard cock..
Finally I heard my father say he was close. She kept riding faster and faster. "I'm going to cum." She cried out. "Cum in me daddy. I want to have your baby. " He let out a massive groan and started to fill her pussy with his hot spunk.
That was it, I began to shoot my load all over the floor, the thought of my dad being the father to his own grandchild had me blowing the biggest load I've ever blown. It went everywhere. I quickly removed my shirt and cleaned up before turning and heading to our room. I couldn't wait for her to return. My heart was pounding in my chest and my cock was still hard as a rock.