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).

“I like everyone to meet each other and be friends and stuff,” he explains.

"There was a side of me that was ecstatic – the teenage boy in me that wants to fuck everything I see," reveals Ryan, a millennial in an open relationship.

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.

"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.This generation is radically rethinking straight sex and marriage, but at what cost?In Part One of a two-part series, Rolling Stone goes under the covers in search of new approaches to intimacy, commitment and hooking up.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.He doesn’t have a long-standing secondary relationship like Leah (“I’ve actually veered away from doing that”), but he certainly enjoys the company of other women, even sometimes when Leah is home.I have couples that have closed relationships or open relationships depending on how they feel about the relative health of their relationship.