Who is your fantasy sexual partner?

Mine is a swimsuit model who makes her own porn. Insatiable. Adventurous. Flat stomach. Yoga-flexible, hangup-free, and orally fixated.

And she’s my actual girlfriend.

I’m not bragging here (okay, maybe a little), because I’m no Calvin Klein model. I’m a divorced father of two in my 40s. My hair is going gray, my skin wrinkling. Natalie, on the other hand, is a decade younger and physically flawless.

When my marriage fell apart, the one silver lining I saw was the possibility of dating a woman like her, someone who would make me feel like a testosterone-crazed teenager all over again. Maybe I’d finally join the Mile High Club.

And then along came Natalie, seemingly heaven-sent. We met at a writing workshop; I was her teacher. For everything in the bedroom, though, I would be the student.

During one of our first sexual encounters, she had her long, tanned legs gymnastically spread in a way that really shouldn’t be anatomically possible, while I went down on her.

When she scissored her legs around my neck, I thought of a nature video of a female praying mantis decapitating her lover during copulation.

“You’re getting, like, 10 percent of me here,” she growled.

I tried to imagine the last 90 percent. Perhaps I should get some rest first.

“I’m in my sexual prime now,” Natalie explained afterward. “You’re not. That’s just reality. I’m not going to be ashamed of my desires. If I want to be pleasured by five men at once, I get to have that fantasy.”

Clearly, it’d be a challenge to go one-on-one with a woman who’s ready to take on a basketball team, and not feel outmanned.

How could I, a mere aging mortal, expect to satisfy this woman’s Olympian desires?

She was also smart, funny, creative, and, compared with other women I’d known during my checkered romantic past, incredibly sane.

I was falling hard and fast. And yet my first declaration of love was met with 24 hours of radio silence.

I killed the time imagining all the ways she could pleasure five men at once. Did I mention that she has uniquely dexterous feet?

She finally called.

“I’ve longed for a man with the courage to claim me for his own.” (Yes, she really talks this way.)

The next day, she christened our commitment by blessing me with the blow job of my life, searching out every nerve ending with surgical precision.

It didn’t occur to me to wonder how many times she must have performed this very operation to become so mad skilled. And really, was it any of my damn business?

“You’re getting maybe 60 percent of me now,” she said one day while we were making love.

Our courtship was still young then, but Natalie’s habit of ranking the intensity of our lovemaking was starting to get old.

“I want all of you,” I huffed, double-timing our pace. Natalie smiled. “Think you’re ready to dance with the dragon?” Ah, maybe.

The dragon soon appeared as a fire-breathing vixen that made inhuman sounds as she raked her nails down my back, drawing blood. Her imagination and hunger seemed limitless.

I would stumble into work late, jelly-legged after being devoured for breakfast.

My first email of the day was often a picture of Natalie touching herself: “Waiting for you. . .” I thought of Nelson Rockefeller and wondered how many men expire during sex every year.

“I punched a man once,” she confessed out of the blue one day. She never hit me, but she did KO my lower back. One morning, after weeks of nightly marathons, I couldn’t get out of bed. It took me two weeks to get back on my feet.

“Fuck me. . .fuck. . .oh god!” Natalie convulsed with a seismic orgasm.

Unfortunately, I hadn’t given it to her. She sighed as she withdrew her White Knight, a pearlescent vibrator a size larger than my own Pink Pawn. We had moved in together, and she’d brought along the Knight and a boxful of other old friends.

“Are you okay?”

I was not. But I also wasn’t going to admit that I felt emasculated by her toys.

“Sweetheart, it’s okay,” she said. “A lot of guys get freaked out by toys.”

“You’ve used toys with a lot of guys?”

Natalie gave me a maternal hug. “Baby, is hearing more about my sexual history really going to be good for you right now?”

“I just don’t want to share what we do in bed with anybody from your past, okay?” I said. “If there’s a toy you’ve had a playdate with before, can you get rid of it?”

Natalie understood—and got rid of her toys. Every last one of them.

“You’ve done this before, haven’t you?” I demanded. “Haven’t you?”

She had. But I had too. And yet my jealousy was getting the best of me.

Natalie covered up and turned off the video camera. We’d shoot no triple-X footage today.

Instead, we agreed to purge all photos and videos of past lovers. I spent an hour rooting through old emails and hard drives. It took Natalie the better part of a day.

“What are you, Pornhub?” I asked.

“I’m a photographer,” she bristled. “I photograph things. I’m only keeping 20 nudes of Nick, but it’s just a work thing—a fine-art project.”

Nick was her most recent ex, with a body apparently suitable for framing. By all accounts, he was a decent man who treated her well.

But even though we’d never met, I couldn’t stand him. I had the feeling that he was in bed with us. I pictured him as a dead ringer for Michelangelo’s David with a Swiss Army sex toy for a penis.

The more I obsessed over getting 100 percent of Natalie, the more I felt I was losing her—and a bit of myself.

Why sneak in the back door when you’ve been invited in the grand entrance? That was my take on anal sex before I met Natalie. But the idea that Nick had explored that part of her made me need to plant my flag there.

“Dude, you should totally tap that,” I imagined Nick saying. “Turns her into an animal.”

I tried, really. But by the time I’d work out the position, I’d lose my erection. Soon it was gone for good.

The truth about erectile dysfunction is that the harder you fight it, the softer you become. I was afraid Natalie would be disappointed; her reaction was worse. She was hurt.

“This always happens,” she wept. “I’m too much for men!”

I saw a therapist who specializes in sexual dysfunction.

“Most men can’t deal with hearing about their partner’s sexual experience unless she’s saying how big or great he is,” she told me. “Remember, no one gets amazing at anything, including sex, without a lot of practice. You should write a thank-you note to every one of her former lovers for all she learned with them.”

Dear Nick: Thank you for not perforating my girlfriend’s colon. . .

Maybe we wouldn’t be pen pals, but I saw the therapist’s point: Loving Natalie meant loving all the experiences that made her the amazing person—and blessed superfreak—she is today.

Natalie wrote NICK in large block letters in the sand. His name joined a long list of our exes scrawled across the beach. As the tide washed the names away, we mentally thanked our exes for all they’d given us.

The therapist had suggested this as a cleansing ritual. It was hokey, but I can’t deny it worked.

I was more accepting of the truth: I wouldn’t be a teenage horndog again. I would never resummit my sexual peak. Maybe I’m even a lousy lay. But none of that changed this: Natalie chose me, wrinkles and all.

After I quit multitasking in bed—giving my ego a hand job while making love to her at the same time—a funny thing happened.

I saw delicious details I’d overlooked.

How caressing the skin behind her knees made her purr like a kitten, how grinding her slow and deep made her yodel with delight, and after all my foreplay, how kneeling in bed with her ankles airborne and thrusting like a freight train made me the little engine that could, 100 percent, take her to the promised land.

I’d be lying if I said that being the first man who could bring her to orgasm without toys or gadgets didn’t bring me a certain pride.

The irony is that my pride nearly ruined it. I’m not the man I used to be, and that’s a good thing. It’s what brought us together, hopefully forever.

Besides, Natalie says my gray hair makes me look like a professor at an oddly specific Ivy League school. The mere thought of it, it turns out, makes her hot for teacher.