She takes the initiative

Surprisingly, your mother escalates things further without any prompting. Breaking off the passionate kiss, she peels her shirt and jeans off with a sense of urgency. That didn't take much... Maybe Mom's a little pent up?

She’s wearing plain white underwear and a matching bra, but she still looks amazing in them. Her tits are slightly smaller than Melanie’s, but her ass is much bigger and rounder. You kick yourself; how did you never notice just how fucking _hot _your mother was?

"Hey Mom... I appreciate the enthusiasm," you grunt as she undresses. "Who knew you were so **** to be my slut?"

"I... I really am," she says, the fire in her eyes growing at your words. "Are you going to use me too? Will you... Um..."

"Of course I'll impregnate you, Mom," you finish for her. You don't know if that's what she was about to say, but it's what she wants now. "It wouldn't be fair if only bred Mommy-slut."

Your mother finishes undressing, watching you plow Melanie all the while. Looking past her to your father, you can tell that he's incredibly uncomfortable.

He gulps as you catch his eye. “Uh, you sure you don't want a little privacy?”

“Sure, Dad," you reply, taking pity on him. "Why don’t you go for a drive? I’ll let you know when I’m finished.” With a relieved nod, your father sidles out the door.

Turning your attention back to Melanie, you hold her down by her arms and begin pumping into her with an increased sense of urgency. “Oh, fuck,” She cries. “Fuck me harder, baby. Let me take care of you... Use your Mommy-slut..."

Your biological mother, now completely nude, kneels down so that her head is level with your dick. Without any encouragement, she begins groping your ass and fondling your swaying ballsack, cooing words of encouragement all the while. “There you go, baby. I know you’ve got enough cum in these big, fat balls to fill us both up...”

At that thought, your dick hardens even more, and you recognize that you’re in danger of cumming already.