"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.

Ryan is a young Generation X’er, while she’s an older Millennial.

While both generations were raised by Baby Boomers – who not only initiated the sexual revolution, making acceptable the concept of sex outside the confines of marriage, but who then went on to mostly pair off in traditional marriages – hers was the generation in which the greatest percentage of those partnerships ended in divorce (the divorce rate peaked in the early Eighties, right around the time it’s believed that the Millennial generation began).

He was therefore surprised when the first thing Leah gave him after the move was a book called Certainly, open heterosexual relationships are nothing new.

Even the term “open relationship” seems like a throwback, uncomfortably reminiscent of free-love hippies, greasy swingers and a general loucheness so overt as to seem almost kitsch.

Or, more specifically, that going outside the partnership for sex does not necessitate a forfeiture of it.

“I was at a practice where we would meet every week, six to eight therapists in a room for teaching purposes and to bring up new things coming into therapy that weren’t there before,” says Lair Torrent, a New York-based marriage and family therapist.

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.

This generation is radically rethinking straight sex and marriage, but at what cost?