From the dog run to Whole Foods to the Apple Store, you don’t have to look far to see single people flirting it up. But when it happens at the playground (where the vast majority of parents are not so single), one tends to want to look away. Once upon a time, I worked with a couple (call them Jack and Jill) who hadn’t had sex in the year since their daughter was born. While Jill “wanted to want sex,” she complained of feeling “touched-out” from breastfeeding and of being too tired for sex. A successful marketing executive, she had returned to work after an all-too-brief maternity leave, while Jack, a freelance writer, stayed home to take care of the baby. Our weekly conversations focused on how sex-starved Joe had been feeling and his anger and humiliation at being constantly rejected. “Every night it’s the same thing: Jill comes home and wants to spend all of her time with the baby, and then is too tired to do anything else –- especially sex. Why step up to bat if you know you’re going to strike out?” he lamented. Just when they started making progress and having sex again, an incident occurred that set them back. Jill had been distracted by Jack’s iPhone buzzing and beeping and, as she turned off the ringer, she took at look at his messages. She was shocked to discover that many of his e-mails and texts with other moms (mainly to make appointments for play dates) had a flirty, chatty energy. “It’s not that they were sexual,” she said, “but they were funny, charming, and flirty - and trying way too hard.” While Jack was furious that Jill had snooped on him and didn’t feel that he was doing anything wrong, he did eventually admit that it was nice to flirt, “and to know that I’m still attractive, at least to someone.” When I was working on the book “Sex and the Baby Years,” I did some informal interviews at local playgrounds. One of the topics was flirtation and infidelity and how dynamics at the playground might have changed with the influx of stay-at-home dads. Said Chloe, a mom of three who had been hitting the same playground for nearly a decade, “It used to be mainly moms and nannies, and maybe the occasional dad. But now there are all these stay-at-home dads and they’re cute and funny and interesting and they want to talk and talk and talk. I used to just throw on sweats and a ratty T-shirt, but now I’m getting dressed up and putting on lipstick and it’s much more of a scene. In many ways, it’s an added pressure.” But Elizabeth, a recently divorced mom, felt different. “I’m 39, with a 4-year-old son,” she explained. “Even when I get a night to myself, I just want to go to the gym and then go to sleep. Really, who’s going to be interested in me? Somebody with his own baggage, like a divorced dad. I’m definitely not looking to bust up any marriages, but I am looking.” “I had to change playgrounds and stop going to group play dates,” said Shannon, a mom in a sexless marriage who wanted to up her passion-quotient, but felt like her husband was depressed and uninterested. “There was a dad who was very forward and cute and I started talking about my issues at home, and I knew I was getting into trouble when I was fantasizing about him and coming up with all of these romantic scenarios. I wasn’t ready to give up on my marriage.” As for the guys I spoke with, many were similar to Jack: stay-at-home dads who were a little bored and very frustrated in their own sex lives. Most flirted for the attention and fun, but a few said that having an affair with a married mom would be perfect - both parties would be in it for the sex and not looking for a relationship, which made the idea all the more alluring. Emotional infidelity has always been a gray area. It usually occurs when a person in a committed relationship forms a deep attachment to someone he or she is attracted to and pursues increasing intimacy, but without sexual activity - at least at the outset. Emotional affairs are often the precursor to full-blown sexual affairs. Today, both men and women are having emotional affairs that start with the heart and the mind. We’re all living, breathing sexual beings. Attraction doesn’t end once we’re in a relationship. Even the most happily coupled people are going to feel the familiar buzz of attraction when someone catches their eye or laughs at one of their jokes. But in her book “Not 'Just Friends,'” Dr. Shirley Glass reported that 82% of unfaithful people started out being acquaintances, neighbors, or co-workers with their affair partners. In other words, people who are unfaithful to their partners weren’t looking for a relationship or seeking out strangers in a bar; it just happened. In my professional experience, parents, especially news ones, are a particularly vulnerable lot: When you have a baby, sex goes from being something that used to be spontaneous to something that goes on a to-do list. And as sex falls to the bottom of that list, relationships become increasingly vulnerable: to anger, resentment, indifference, and, yes, infidelity. No wonder a recent study from the University of Denver reports that 90% of new parents experi­ence a significant decline in relationship satisfaction, or that, according to a recent survey by the online magazine Baby Talk, just 24% of parents say they’re satisfied with their post-baby sex lives, compared with 66% who were happy before they had children. Flirting a little is a natural part of life. And many couples are able to channel that energy into their own relationships. But when flirting doesn’t get re-directed into the relationship, but rather is re-circulated outside the relationship, the air at home tends to get stale. For parents who feel like they’re more connected to their peers than their partners, it’s probably time for a trip to the playground - together!