Flip her over.

You kiss your way back up her chest and neck and to her soft lips. She seems much more warmed up now, kissing you harder than before and grinding her hips against you. You think she's finally ready for the main course - and you know you are. You grab her arm and flip her over into a prone position, eliciting a soft, surprised gasp from her. You pull her one-piece off the rest of the way, exposing her perfectly round ass.

Then you slide your own swimsuit off. Sarah eyes your cock and subconsciously begins wiggling her ass and biting her lip. Well, it's hard to get a lot clearer than that. You hop back on top of her, straddling her thighs. You line up your cock with her pussy and slowly slide in. She's wet enough that you have no trouble sinking your entire cock inside her, and a moan escapes both of your lips.

"God, that feels so good," she half-whispers, half-moans. You're inclined to agree. You begin thrusting, starting slow and building up your speed. One hand grabs her bare shoulder for some leverage and the other grabs a fistful of her ass and squeezes it as you start to pound her pussy in earnest.

Sarah buries her face in the mattress in an attempt to muffle her cries of pleasure and holds the bed sheets in a white-knuckled grip. You use the hand gripping her shoulder to pull her into each thrust, plunging deep inside her at a steady rhythm. A muffled sound escapes her mouth every time you bottom out in her, your hips slamming into her ass.

Careful not to break your rhythm, you use the hand that isn't gripping her shoulder to give her a good spank. She yelps in surprise but raises no objections, so you smack her ass again, slightly harder this time. "Harder," she manages to say. You slap her ass even harder than before. "Just like that," she cries out. You keep hammering her pussy and spanking her, making sure to switch between her cheeks for a bit of a reprieve. She seems to lose herself to the haze of pleasure, her brain shutting down, her moans starting to blend into each other, her gorgeous body going more limp.

Partially because it's hot and partially because you want to make sure she can still breathe with her head buried in the mattress, you give her ass a break and use your free hand to grab her hair by the roots and pull her head up. Her moaning gets louder, though you can't be entirely sure it's from her liking having her hair pulled and not just because she's not being muffled by the mattress anymore. But you suspect it's the former.

After a few more minutes of thrusting, you feel her muscles start to tense up underneath you, her hips involuntarily bucking slightly. Sensing that she's getting close to an orgasm, you keep hammering away at as steady a rate as you can maintain. You only hope you can make her cum before you do.

You manage to do just that. Waves of pleasure ripple through her body as she screams out, loud enough that you're worried that the others could hear, on the chance they'd come inside. Her noises are so hot, you feel yourself approaching the brink as she starts to come down from her own climax. You let go of her hair and use both arms to brace yourself for the home stretch.

"I think I'm about to cum," you say as her body relaxes again underneath yours.

"No, wait," Sarah says, snapping back to reality somewhat. Her voice still sounds a bit dazed, though. "You can't cum inside me, I'm not on birth control."

Welp. You're certainly not going to cum inside her after she told you not to, so you stop thrusting and sit back for a moment.

"Do you want to cum in my mouth?" she offers. "I can suck you off until you finish. I just need a couple minutes to recover first."