I have couples that have closed relationships or open relationships depending on how they feel about the relative health of their relationship.It’s not so dogmatic.” It’s worth noting that their arrangement was ultimately Leah’s idea.Ryan is a young Generation X’er, while she’s an older Millennial.

By the end of their dinner at a small Italian restaurant in New York’s West Village, Leah is getting antsy to part ways with her boyfriend Ryan, so that she can go meet up with her boyfriend Jim.

It’s not that she means to be rude, it’s just that Jim has been traveling for work, so it’s been a while since she’s seen him. As her “primary partner” and the man with whom she lives, he is the recipient of most of Leah’s attention, sexual and otherwise, but he understands her need to seek companionship from other quarters roughly one night a week.

"But the other side of me was concerned about what this means in terms of intimacy and how the dynamics would work." When Leah and Ryan met at a wedding four years ago, they didn’t expect to develop this type of arrangement.

Neither of them had had an open relationship before, though it was something that Leah had contemplated.

But Leah and Ryan, 32 and 38, respectively, don’t fit these preconceived ideas. She wears pretty skirts; he wears jeans and trendy glasses.

They have a large, downtown apartment with a sweeping view and are possessed of the type of hip hyperawareness that lets them head off any assumptions as to what their arrangement might entail.

“I remember the first night, I was telling him about my difficulty with monogamy,” she says.

“I don’t know why I felt the need, but it must have been on my mind a lot.” In almost every relationship she’d had, she’d found herself cheating, though she didn’t know if this was a character flaw or a problem with the conventional system. “I was just trying to get into your panties,” he says to her, laughing.

And in this, Millennials realize that they’re pushing the boundaries of the sexual revolution beyond what their parents might have expected and their grandparents could even conceive.

By and large, Leah and Ryan feel comfortable with friends their age knowing that they sleep with other people, but are not as comfortable telling older people (for this reason, and for fear of professional repercussions, they’ve asked me to change their names for this article).

Tonight is one of those nights, and soon Leah will head to Jim’s penthouse apartment, where the rest of the evening, she says, will probably entail “hanging out, watching something, having sex.” “She’ll usually spend the night,” Ryan adds nonchalantly, which gives him a chance to enjoy some time alone or even invite another woman over.