Whether they call it a “starter” marriage, “beta” marriage or “test” marriage, the 25- to 35-year-old generation has a far more elastic definition of the concept of “forever.” How elastic? A recent study found that 43 percent of millennials supported a form of marriage that allowed couples to easily split up after two years, while a full third were open to “marriage licenses” valid — like mortgages — for set periods of time. It’s an impressive figure, especially when you consider just a third of respondents still believe that marriage is “till death do us part.” So what’s going on here? Have social media and dating apps killed off marriage? Or has digital culture — if not hook-up culture — so spoiled young people for choice that they’re simply unable to settle down? With same-sex marriage now legal, has making marriage more inclusive eroded its traditional sense of exclusivity? Or are millennials merely early-adopting a future where marriage is unnecessary? Part of the problem is role models. Just 26 percent of millennials are married, according to a landmark Pew Center report, compared to 36 percent of Gen X-ers 20 years ago — and 48 percent of boomers back in 1980. Millennials are also among the least religious Americans ever — with a full third unaffiliated with any single faith. In fact, a lack of faith is, perhaps, the most defining millennial characteristic: Just 19 percent of them believe that most people can be trusted.