I switched back every three minutes or so, enough to tease both girls into a frenzy without finishing myself off. But after the first half-dozen switches, I started to let them cum. Whichever girl was left alone would play with herself and also caress the body of whoever I was fucking at the time, my cock and her girlfriend triggering exquisite orgasms in the receivers.

And then, at last, I got Cherys off one more time, her back arching as she howled her climax into Danielle's open mouth. In a fluid motion I pulled out and thrust into Danielle, rapidly pounding my sister until she reached her crescendo, screaming my name and clawing my back as I filled her with my incestuous seed.

“YES!!! Fill me up baby brother!" Danielle cried out, ecstatically happy as she felt my hot cum pulsing against her inner walls as she met me with an orgasmic flow of her own.

When we were done, she held my dead weight to her, rubbing my back proudly.

“Good boy..." she cooed.

I smirked in my post-coital stupor. In was an interesting dynamic fucking your older sister.

“It's really too bad you can't knock me up. I wonder what it would be like to have your baby..." Danielle rubbed my head. I just shrugged. It was a chance we couldn't take and it was a line I simply would not cross. There would just be too many awkward questions and I couldn't imagine what life would be like for that kind of kid. I personally made sure Danielle was taking her pills every day.

But just when my sister seemed to be drifting towards melancholy, I kissed her and then said softly, “Time to clean up for round 2." Danielle's emerald eyes lit up like Christmas as she rolled me off her and then turned to straddle Cherys' face, careful to keep one hand pinching her pussy lips together, Meanwhile, I moved to the headboard to sit up and cool off. Cherys reached out and guided Danielle's thighs into position, and then she gaped her mouth open wide as Danielle released our mingled cum down into her lover's open mouth.

While Cherys was busy slurping at her snatch, Danielle then bent over onto all fours between my legs, holding my softening cock between her thumb and forefinger. And then she went down to suck me clean of our juices.

Danielle had been practicing her oral skills on me quite a bit in the past month or so. Cherys had been teaching her new techniques and then assigning Danielle “homework for the times when she herself was fighting bouts of morning sickness or otherwise feeling like crap. That was one of the downsides to Cherys being pregnant. Sometimes she was so horny she would fuck me within an inch of my life. Other times, she felt so shitty I couldn't even touch her body without her snapping at me like she had the worst case of PMS.

Fortunately, today was one of the horny days, and once Danielle had me fully erect for another go, Cherys snagged the bottle of Astroglide out of the bedside table and then got onto all fours.

“I feel like a good assfucking, David," she husked at me.

Sounded like a plan to me.

“Me, too," Danielle said shyly.

Cherys and I both snapped our heads around to her. Cherys had briefly proposed the idea a few weeks ago, but at the time, Danielle had been seized by a flashback to her rape and practically gone catatonic for an hour. We'd carefully avoided it since.

Danielle looked us both in the eye.

"I want David in my ass too. I don't want that monster to have been the only one back there anymore." And with that, Danielle got onto all fours side-by-side with Cherys, their hips touching together.

I stared at two gorgeous asses, pink rosebuds winking at me enticingly. Cherys' ass was fuller and rounder, but no less firm than Danielle's more svelte figure. Just minutes before, they'd been side-by-side with pussies spread wide for me. Now I was getting a repeat from the other direction. I coated two fingers on both hands with the lube and settled behind the girls. Danielle was a little tense, but Cherys just shivered in anticipation. Index fingers pointed out at the same time, briefly touching each anus before slipping in to a chorus of gasps from both girls.

Here I was, with my fingers up the butts of two beautiful young women. I had found heaven on earth. Or hell. Either way, it promised to be a wild ride.

Cherys was moaning by the time I pushed in the second finger, but Danielle was still tense. I was going to have to work a little harder to relax her, and I decided that I would start with my cock in Cherys first while I warmed Danielle up for the big event.

I lubed myself up and then shifted so that I was behind Cherys, grasping her hip in my left hand while my right stayed wriggling in Danielle's ass. The hard helmet of my cock pointed the way to her red star.

“Wait, not yet," Cherys broke my reverie and she moved out of position, much to my disappointment.

“You should do Danielle first. And I'll help you."

With that, Cherys flopped onto her back and then snaked her way backwards until she was in a relative sixty-nine with Danielle, her head between her girlfriend's knees as she looked up into her lover's pussy. She began by pulling Danielle's hips down so she could take a slow lick along her lover's cleft, and with a low moan my sister dropped her crotch the rest of the way so that Cherys could feast upon her.

Danielle started to relax as she felt the familiar pleasure washing through her. Cherys' talented tongue knew all of Danielle's buttons, and by the time Cherys reached around to pop her own finger up Danielle's lubricated asshole, my sister was sufficiently relaxed that her anal passage provided minimal resistance to the invading digit.