She issues an invitation

When you pull out of Deborah's quivering body she slumps onto the bed, gasping softly, looking up at you with drowsy eyes.

"You fucked me so good!" she purrs. "I needed that so much! Too long since I've had a hard cock in me. You can stay the night if you want Mason. Wake me up in the middle of the night and bang my brains out again, and fuck me silly in the morning. I'd love that."

You consider her invitation, remembering that you had told Brian you would take him to the meeting of the mysterious group you discovered last night. If you stay with Deborah, you'll have to forego that, or he will have to go on his own.

On the other hand, if you stay with Deborah you'll have the pleasure of fucking her senseless, which as you've already discovered is a very rewarding experience.