Consider this post from Michael Krueger about the history of Christianity with respect to sex, love and marriage.
[I]n the second century, as Christianity emerged with a distinctive religious identity, the surrounding pagan culture began to take notice. And it didn’t like what it saw. Christians were seen as strange and superstitious–a peculiar religious movement that undermined the norms of a decent society. Christians were, well, different.
So, what was so different about Christians compared to the surrounding Greco-Roman culture?
[…]While it was not unusual for Roman citizens to have multiple sexual partners, homosexual encounters, and engagement with temple prostitutes, Christians stood out precisely because of their refusal to engage in these practices.
For instance, Tertullian goes to great lengths to defend the legitimacy of Christianity by pointing out how Christians are generous and share their resources with all those in need. But, then he says, “One in mind and soul, we do not hesitate to share our earthly goods with one another. All things are common among us but our wives” (Apol. 39). Why does he say this? Because, in the Greco-Roman world, it was not unusual for people to share their spouses with each other.
In the second-century Epistle to Diognetus, the author goes out of his way to declare how normal Christians are in regard to what they wear, what they eat, and how they participate in society. However, he then says, “[Christians] share their meals, but not their sexual partners” (Diogn. 5.7). Again, this is the trait that makes Christians different.
We see this play out again in the second-century Apology of Aristides. Aristides defends the legitimacy of the Christian faith to the emperor Hadrian by pointing out how Christians “do not commit adultery nor fornication” and “their men keep themselves from every unlawful union” (15).
A final example comes from the second-century apology of Minucius Felix. In his defense to Octavius, he contrasts the sexual ethic of the pagan world with that of Christians:
Among the Persians, a promiscuous association between sons and mothers is allowed. Marriages with sisters are legitimate among the Egyptians and in Athens. Your records and your tragedies, which you both read and hear with pleasure, glory in incests: thus also you worship incestuous gods, who have intercourse with mothers, with daughters, with sisters. With reason, therefore, is incest frequently detected among you, and is continually permitted. Miserable men, you may even, without knowing it, rush into what is unlawful: since you scatter your lusts promiscuously, since you everywhere beget children, since you frequently expose even those who are born at home to the mercy of others, it is inevitable that you must come back to your own children, and stray to your own offspring. Thus you continue the story of incest, even although you have no consciousness of your crime. But we maintain our modesty not in appearance, but in our heart we gladly abide by the bond of a single marriage; in the desire of procreating, we know either one wife, or none at all (31).
The genius of Christ-centered relationships is that both parties have to prove that they can be faithful and committed during the courtship. Both people have to work before the marriage to demonstrate their ability at marital roles (husband or wife, father or mother). It’s not just that this is the way that we have always done it, it’s that there are real reasons why chastity and fidelity are important for marriage success. You can’t just have fun, pick anyone you like, and have marriage “work out”. You have to be comfortable with chastity and fidelity, and the person you choose has to be comfortable with chastity and fidelity. Each person has to demonstrate that they are capable of self-sacrificial love for others, since that’s the main thing that marriage is about – at least the ones that last. Virtue is at the center of the Christian concept of marriage.