How do you know it was looser before the Victorian time?
First, British sexual morality post-Restoration is often described as being defined by (or at least "bounded by") the extremes of Puritanism and Libertinism, with the Puritan sexual ethics and the idealization of the purity of women and the corruption of sex eventually winning the day. The Victorian Era sexual morality is often thought of as the long, but slow ascendancy of the prudish ideal. It was an age when it was impolite and scandalous to speak about the body in frank terms. The word "leg" was considered risqué (I am not kidding) they preferred the less sexually provocative term "limb." Even
within marriage sex was supposedly (at least openly in polite circles) treated as if it were an obligation to be detested, hence the story about Queen Victoria telling her own daughter about sex on the night before the daughter's wedding where she supposedly advised, "Just close your eyes and think of England." It was also the age that invented this little lovely, to prevent nocturnal emissions:
Just slip that around your little friend, and the "sin" of your nightly erections would be held at bay.
Second, consider England during the Renaissance and earlier. In those periods most families had one or two beds, and most only one. (Indeed, throughout much of the medieval period serfs and yeoman had only a single room for them, their families and their farm animals.) You had to be reasonably well off to afford multiple beds and multi-room houses (though they were more common in towns than in the countryside, most people lived in the countryside). For those with one bed, all the family slept in the same bed, and many families were large. It's fairly well known at this point that there was no taboo on parents having sex while in the same bed as their sleeping (and likely not quite sleeping) children. When the taboo developed I am not certain, but it was well in place by the time Victorian Era was in high gear.
Not to oversimplify, though, as even in Victorian England, the "working classes" tended to live in one or two rooms and likely has similar social norms to those who came before them. The wealthier chroniclers of the period, who noted the poverty of the working classes, were often quick to note that the working class neighborhoods and lifestyle were havens of "sin" precisely because the poor did not live up up the standards of the bourgeois (and only the wealthier bourgeois had any time to take up "writing" as a significant pastime. Still, over time, even amongst the poor the Victorian zeitgeist descended over most people in England (and many beyond it, including in America, where "legs" were so scandalous, that reports were that Americans invested table skirts to cover them and thus prevent impure thoughts that might come from looking at curved and shapely table legs. (I am still not making this up, though the reasons for the invention of the table skirt may be apocryphal, that explanation as in circulation in England.) The lower classes may not have lived up to teh ideals to the same extent as the upper classes, but they were influenced by them.
In fact you can find entire books and articles about the views of sex and sexuality in Georgian and Regency England that are clear that it was a progression of social attitudes that led to what we tend to think of as the Victorian attitude. Georgian and Regency London, for example, were awash in brothels and pornographic bookstores that were chased away by the Victorians.
It was definitely not a long-standing attitude that later came to be called "Victorian" yet existed all along. It was a developing social trend that, only at its height, became what we call "Victorian."
Not so long ago Rome fell when morality became optional. I'm not saying Romans were moral saints but they were morally astute.
The reasons for the decline of Rome are too complex to deal with here (indeed there are hundreds of volumes of books on the subject). But I think you may misunderstand the "moral decay" argument, which originates (at least the phrase does) with the renowned historian Edward Gibbon.
I also think it's a mistake to assume that it was some "deviancy" of Rome that led to its downfall. The Romans were, by Christian standards,
far more deviant in the
early Empire and during the Republic, than they were in the late Empire...as by then they *were* Christians. It was Christian Empire. Western Rome fell for a variety of reasons, but the power of "Rome" the Empire had long since moved to its new capital in Constantinople (and the "Eastern Roman Empire, the real heir of the strength of "Rome," lasted until 1453 A.D.).
Gibbon felt that the "moral decay" was a loss of "civic virtue" led to the decline (not sexual virtue or even "moral virtue" in a broad sense, as he was well aware the Romans were Christians...indeed he felt that was a large part of the problem). By that, he meant that they started entrusting others to do everything for them, like fight in their military and tend their fields and build new buildings. Gibbon's theory of moral decay blamed (in part, at least)
Christianity for the problem, as he felt it may have led the Romans to care less about their Empire and common, work-a-day concerns than they were with getting into heaven and living their lives for God before the end of the world, which many early Christians thought was coming in the near term, rather than millennia after the death of Christ.) In Gibbon's view, the "moral decay" was a lethargy that he felt became pervasive. As he wrote:
As the happiness of a future life is the great object of religion, we may hear without surprise or scandal that the introduction, or at least the abuse of Christianity, had some influence on the decline and fall of the Roman empire. The clergy successfully preached the doctrines of patience and pusillanimity; the active virtues of society were discouraged; and the last remains of military spirit were buried in the cloister: a large portion of public and private wealth was consecrated to the specious demands of charity and devotion; and the soldiers' pay was lavished on the useless multitudes of both sexes who could only plead the merits of abstinence and chastity. . . . The sacred indolence of the monks was devoutly embraced by a servile and effeminate age.
The "moral decay" of Rome was there were too many people who were abstinent and chaste, and too few who were able to wield a spear.
To take one quick look at another of the (many) theories for the decline the western empire apart from lethargy, the barbarians had been pushed systematically west and wanted to settle on Roman land, and the eastern empire increasingly found that the western empire was costing them more money than the land was generating. The Eastern Empire became less and less engaged with the west over time, and the east had all the money and power. The result was that the western provinces of Rome *had* to fend for themselves, because the western empire had no resources to spare for them. They were increasingly being run by former generals, who were generally German barbarians, but that is not to say that they were not a part of the Empire. The barbarians definitely thought of themselves as local rulers tending to a part of the Empire. Even Odoacer, who deposed the last generally recognized western emperor pledged himself to the eastern emperor and thought of himself as ruling, in essence, a client state in orbit of (eastern) Rome. At least some of the successors of Odoacer thought the same thing.
The odd truth is that the west didn't seemingly realize that Rome "fell" for a couple of centuries. It seems clear that when Charlemagne was crowned emperor that he and many in his court were not necessarily aping some long vanished tradition of the Romans in hopes of evoking its spirit. Rome was a still existing entity in the minds of many at the time. All that had vanished was the western Emperor, but he'd always had limited power and really was subject to the stronger Eastern Empire. By invoking the imperial title in the minds of some he was arguably reestablishing
an office in the still existing empire, not forming a new empire in the image of the old one. In retrospect, he was forming a new empire, but Rome vanished so gradually, that there were those who didn't see that at the time.
So goes the theory, at least, and there is at least a solid argument for it.