Find somewhere private.

"Let's go outside then," you say. Grace's patio has a small overhang where the others won't be able to see you from upstairs and the privacy fence around the yard is tall enough to block the neighbors.

Sarah looks hesitant but nods her head. You take her by the hand and lead her out the backdoor, closing it softly behind you. The furniture out here is as lacking as the rest of the house, but luckily Grace did get a couple pool chairs. You adjust the back of the chair so it's flat like a bed and then lay down on it. You pull Sarah on top of you into a straddle.

She leans in for a kiss and slowly starts grinding her hips against you as you make out. You're already hard and feeling her press against your cock feels amazing. You slide your hands down her body and start squeezing her ass. She giggles softly. "Someone likes my butt."

"In my defense, your butt started it on that couch."

She giggles again. "I guess it did, huh?" She sits up. "Want a better view of it?" Without waiting for an answer, she turns around. She's still straddling you, both of you still clothed, but in a reverse-cowgirl position. She starts grinding on your cock. You can't hold back a moan, at the sensation and view. You start squeezing her ass with both hands.

"Mmmm, you like this, huh? I do too."

You respond by lightly smacking her ass. She giggles and says, "Quiet! Wouldn't want the others hearing, would we?" Getting caught fucking your hot friend's hot friend by said hot friend and her other hot friend doesn't sound that bad to you, but you keep your mouth shut. You go back to squeezing her butt and she keeps grinding.

Then, she says, "I think I might want something more soon, though, what about you?"

An excellent question.