Once she says what you want to hear.

You lean in closer to Megan and touch her shoulder.
You whisper the word 'trance' and she goes under.

"Deep down, you love to fuck me and share your friends with me to fuck together. I won't need to tell you to bring them over.
You'll do this and won't wonder why. Say 'yes' if you agree."
"...Yes."

You release her from the trance and tell her to cum.
As she does so, she grabs you and kisses you passionately!

Rachel cums as her body betrays her.

"I think you need to pay her back for that licking now," you say.
"I agree," Megan says, her conditioning working well, "Of course, you know what else I want."
"I think we can accommodate that. Right, Rachel?"
"I think so..."

Rachel moves to the other end of the bed, while you and Megan switch as well.
Your roommate moves into position on her stomach in front of her friend, ready to pleasure her.

Before that, however, she spreads her ass cheeks as the invitation for you to fuck her.
You take said invitation...

You start to fuck Megan as she keeps her friend happy.

You know that she wasn't openly-bisexual before...but she must have had some lesbian experience in her past.

How else do you explain her being so good at licking out Rachel that she just can't stop cumming?

Megan shakes her hips at you as her tell that she's going to cum.
There's plenty of shaking going on!

As this keeps going, you wonder how long you can keep up with these two...