Here's another woman he likes, pictured with a horse bit in her mouth. “She's a dance instructor,” Dave says. “She's fantastic, such a fun fuck.”

He stops on an average-looking couple and says this husband's thing is inviting three or four guys to a secluded park bench, where the excitement is heightened by the possibility of being seen or caught—and not just for the husband's pleasure, that's for sure. “She loves it,” Dave says fondly. “She's a little slut.”

Of course, there are a few weirdos. Sometimes the husband seems to be forcing his wife into it, and Dave won't cooperate with that. There was also a couple who had a 6-year-old asleep in the next room, which was just wrong. But this couple—he clicks on another set of pictures—really surprised him. Everything was totally normal at first: “Dude takes his shirt off, and he's got the SS on his chest, he's got other Nazi symbols, and I'm looking around, waiting to get jumped.” But the husband quickly explained that he'd been in prison and only got the tattoos to survive. Dave shakes his head and laughs. “The things I've seen!”

The real secret to Dave's popularity is simple. He loves women. A lot of men say this but find all sorts of flaws in the actual women they might otherwise end up bedding. But Dave really does have something good to say about every single woman he sees. The truth of this is on display one night at a local pickup bar. A statuesque older blonde walks by, probably 60 and a bit leathery from the Arizona sun. “Ooh, sexy lady,” he whispers. I watch him ogle another woman, this one in her 50s, also a bit haggard but dressed in tight clothes and large in the chest. “Love it! Jesus!” The seriously overweight woman heading to the bathroom also gets his nod of approval. “Great ass on her,” he says. “Woo!”

The waitress comes over to get a drink order. Dave asks for her name and flirts for a while, getting a smile out of her. He shakes his head in appreciation as she walks away. “She's hot.”

She was not hot. She was bony and plain and possibly anemic, her skin so wan it seemed to be giving up. But Dave disagrees. She had a beautiful smile, he says. You could tell she had a sweet nature. And this is another thing he's learned—at the beginning of his adventures, looks mattered much more. He was always after the 10s (“dimes,” he calls them). But wide experience has changed his views. Women with looks out of a magazine can be boring in bed, while an older woman or a bigger woman can be tons of fun. What he likes now is confidence. If a woman carries herself like she knows she's got it, that's always exciting.

Another night, he takes me along to dinner with a couple well into their 60s. The husband is a bald grandpa, but the wife is a vibrant redhead in a plunging black evening dress, with a silver necklace and like-colored hoop earrings. Seen through ordinary eyes, she's an attractive grandmother. Seen through Dave's eyes, she's hot.

All these couples have known one another for years, and every few weeks they have a sex party. Dave is one of the very few single guys who ever get invited. He's proven himself, all the women agree.

Like most people in this subculture, the couple love telling their conversion story. They fantasized about sexual adventure for years, but they had six kids and prominent careers back east, and there was no Internet to make things easy. Then they retired to a Phoenix suburb, and right away, the husband got cancer. “I figured, maybe we have a year,” he says. “Let's have fun.”

They started on Craigslist and found their way to more specialized sites; soon they were in contact with 500 couples and 150 single men. Seven years later, the husband's cancer is in remission and they run the most popular sex party in the area, with Dave a much desired guest. All of this is a complete secret from their children, of course, several of whom are conservatives, including one who became a deacon in a Southern Baptist church. “If I want drama,” the wife says, “I'll call my children.”

After a few glasses of wine, her eyes turn soft and flirty and her attention moves completely to Dave. “You only came to one party and you disappeared,” she says.

“You found me,” he answers.

She smiles at the memory.

Then she pouts. “I haven't seen you at the gym lately, either,” she says. “I miss seeing you do those dips in the weight belt.”

Her husband watches, grinning.

Brian Stauffer

Friday night, Dave goes to an orgy. He meets his partners beforehand at a restaurant called Aunt Chilada's. The women are lively and sly, their husbands sitting back in the way of generous fellows who just want to let the party happen. They're all in their late 30s or early 40s and fairly attractive, the extra pounds offset by silky blouses and fetish heels. Lizzie's been married 16 years, has three kids, and works at a local magazine. Tony's a district trainer for a security company. Jack is a geologist. Colin's a financial analyst. The most talkative is Red, a lively nurse who has four kids with Tony. They got started in this nine years ago, she says, because she kissed a girl when she was a teenager and wanted to try it again.

Tony laughs. “I'm sitting there saying to myself, ‘Really? All this time I've been havin' fantasies, and you didn't tell me?’ ”

Red rolls her eyes. “He's such an asshole, but I love him.”

Jane is an actual schoolteacher, having taught third grade for 15 years. She notices that everyone ordered beef. “We like beef,” she says with a wink.

Uber, But for Sex with Clowns Not into the “hotwifing” scene of Dr. Dave? Modern tech offers a community for every desire! Balloonfetish.org

Sexual arousal in the form of blowing up, sitting on, and/or popping balloons. FursForChrist.com

Into anthropomorphic animals? Also a Christian? Purrrfect. TheAtlasphere.com

For fans of Ayn Rand to meet, date, and yell about The Fountainhead. ClownDating.com

“Everybody loves a clown… Let a clown love you.” Dead-meet.com

Dating and networking for death-industry professionals. DailyDiapers.com

Must be over the age of 18. And really like diapers. StachePassions.com

Would've been huge in the '70s. Probably still huge for Burt Reynolds.

“I don't deny it,” says a woman named Marie, a petite brunette who looks French. Her husband, Jack, has tribal tattoos on his arm and the sun-bleached hair of a surfer. They met five years ago at a four-way with her then boyfriend and his then wife, Marie says, and the vibe was so good they started meeting on the side. They've been married for four years, but they both still love to swing. “We can go for months, and we have other things in life that are more important,” Jack says. “We don't need to do this.”

“But we can,” Marie says.

“When we get the itch.”

All these couples have known one another for years, and every few weeks they have a sex party. Dave is one of the very few single guys who ever get invited. Too many others are creepy or cocky, and not cocky in the right way. But Dave has proven himself, all the women agree. He's not a pervert, he isn't trying to take anyone's wife, and he knows how to wait for the invitation. “He's never overly aggressive,” Red says.

Now it's after nine, and a sense of urgency disturbs the group. They start gathering their coats and possessions. A hotel room has been booked. They've done this so many times that they even have a code phrase: “Get dirty by 9:30,” Red says.

The next day, Dave tells me the story of what happened at the hotel. First, Tony grabbed Colin's wife, and they went into the bedroom and the smacking and moaning started; then Dave played with Karen for about an hour, and he was about to leave when Red scooped up his pants. “You're not leaving till you fuck me,” she said, disappearing into the kitchen. But then she got pulled into the bedroom by Melissa's husband, and Jane said she'd tell Dave where his clothes were if he fucked her, so he did that, and finally Jane led him to the refrigerator—his pants were sitting on top of a tray of ice cubes. Man, they were cold! First time he ever saw the benefit of saggy pants!

Dave doesn't have any real guilt about his lifestyle, he insists. He even told his parents. Now when he's going out for the evening, his mother asks him, “Are you going out with your regular friends or your special friends?” And it's more than sex, it really is. A lot of people ask him why he's not married, and sometimes he wonders the same thing, but the truth is, he's stopped looking. After so many years, most of his real friends are his special friends. They go hiking, cook dinner, walk the dogs, hang out. In fact, when he got to the orgy last night, Red was out on the balcony crying about some sibling conflicts among her kids, and he calmed her down. In the morning, he checked in to see how things were going. Look, here's her response:

It sucks. Thanks for caring, you're amazing. XOXO.

And he really does believe he is helping people's marriages. Many times, a husband has told him, “I mentioned you in bed last night and she fucked the living shit out of me.” He loves that. And he appreciates when couples credit their time with him to better intimacy and communication with each other. He also loves the T-shirts that say IT'S NOT CHEATING IF MY HUSBAND WATCHES. “That's awesome,” he says. “That's true.” There's just something about three people sharing such an intimate thing, each for their own reasons but all together in the moment. (Dave doesn't have sex with men, but he's not uptight if there's a little incidental contact with a husband who gets close.) He actually feels bad that he can't be so generous himself; on the one occasion when he was dating a woman who wanted to try a three-way, he got a twinge of jealousy that freaked him out. “It threatens me,” he admits. “It's kind of barbaric. I'm very envious of the husbands that don't have that ego.”

Dave pours himself a glass of bourbon and downs a fat herbal pill—better than Viagra, he says. “It keeps me going for four days. The only drawback is it makes your vision kind of funny.”

He sometimes feels strange that he's not sleeping with more black women, but there aren't many in Arizona. Plus, he says, most black guys don't like to share, and there are just so many adventurous white couples.

But enough talking. It's time to get ready for tonight's adventure—the date with that Christian couple who've been together since they were 19: Jenny and Leon. Dave takes a shower and puts on some nice slacks and a dark shirt, then pours himself a glass of bourbon and downs a fat herbal pill—better than Viagra, he says, and you can buy it without a prescription at any porn shop. “It keeps me going for four days. The only drawback is it makes your vision kind of funny.”

Half an hour later, Dave is waiting in a leather booth at a lively local bar, studying the parking lot through the window. “There they are,” he finally says. That must be Leon in the blue golf shirt. He looks, it must be said, like Robert Carradine in Revenge of the Nerds. Jenny is wearing an orange dress, as promised. She has apple cheeks and an upturned nose, eyeglasses and strawberry-blonde bangs, the cute girl from middle school mellowed into a sweet, homey mom.

Dave goes to meet them at the door, shaking Leon's hand first. (As he previously explained, acknowledging the husband first is Gigolo 101.) In the booth, Jenny is silent and seems very shy, huddling against Leon while he tells stories about the guys they've met before, including one who wanted to meet them at a dog park but didn't bring a dog. Another guy's screen name was Donkey Kong.

Dave laughs. “Oh, my God! Really?”