Stick to the plan

You sit up, give Nyx a quick grope, and say, "Selene, get on your hands and knees. She immediately does so, not wanting to displease you. You move in behind her.

Her ass is absolutely amazing- two plump round cheeks without blemish or imperfection. It might be the best you've ever seen, except possibly Doe, but that was so long ago that you can barely remember it. "She has a nice ass, doesn't she Master?" Nyx purrs, leaning in to place a kiss on the left cheek.

You raise an eyebrow at the word 'Master', but just reply, "Very nice. One of the nicest I've ever seen."

"I can't wait to see you take her from behind, Master."

"Well don't worry- you won't have to." And with that you push forward and penetrate Selene. A cry of contented joy escapes her lips. You start to thrust into her, slowly at first, then faster as she becomes accustomed to your gigantic dick; it also helps that she's sopping wet.

Both yourself and Nyx watch transfixed as your abs smack against Selene's perfect ass, making it shake and quiver. You grab a handful of that shivering flesh and squeeze it between your fingers. Nyx reaches over too and strokes it. "Such a beautiful ass..." she whispers.

"Oh Master, I'm so glad I please you," Selene whimpers. "You make me feel so good! Oh, gods!"

Hemera has managed to collect herself by this point, and she crawls around to Selene's head and gives her a long, deep kiss. Then she positions herself so that she's on her back with her legs splayed, her pussy laid open for the other blonde. Selene obligingly dives in, putting her head to that cleft and sticking her tongue deep into Hemera's cunt.

"Ooh, yes!" says Hemera. "Eat me out, Selene! Pleasure me as you pleasure our master!"

You keep fucking away at Selene almost brutally, delighting in how her ass shudders at your every thrust. Nyx lies down and slides under Selene, and a second later you feel her tongue licking away at your balls as they sway. Then her tongue moves on to the base of your cock and Selene's clit so that she can use it one the both of you at the same time.

You go into overdrive now, slamming Selene for all you're worth. She's moaning into Hemera's snatch; Hemera is groaning and twisting her own nipples for added stimulation. Nyx is somewhere underneath Selene, all of her concentration bent on what she's doing with her tongue.

It's too much. With a roar you start to come, shooting deep into Selene. She in turn, feeling this, squeals and climaxes herself, and Hemera follows soon after. The three of you are lost to bliss for a while then finally return to the real world of the cum-spattered bed.