The first thing you have to realize when approaching this question is that before about mid-17th century (1650) or so, sexuality and sexual identity was largely controlled/supported by the village or town community. People who fell out of line from what was seen as correct or right were often beaten, humiliated or even tried by their local communities. As Stone puts it:

During the late sixteenth and early seventeenth centuries, this intrusive scrutiny actually intensified due to the rise of ethical Puritanism and the increased activity of the Church courts in controlling personal morality. Everyone gossiped freely about the most intimate details of domestic relations, and did not hesitate to denounce violations of community norms to an archdeacon's visitation enquiry, so that people were constantly testifying in court about the alleged moral peccadilloes of their neighbours.

Aside from church courts, and indeed some of the court’s sentences were town humiliations. One such sentence or community punishment might be the use of the cucking/ducking stool—which looked like this or this where the cuckold or the woman accused of being too dominant and controlling or argumentative would be ducked in the water.. the 1615 ballad Cucking of a Scold recounts one such event:

Then was the Scold herself,

In a wheelbarrow brought,

Stripped naked to the smock,

As in that case she ought:

Neats tongues about her neck

Were hung in open show;

And thus unto the cucking stool

This famous scold did go.

The tradition or punishment is quite old--there are references to it in Anglo-Saxon times. The other form of community punishment might be the Charivari or Skimmington ride, that would include a impropmptu town parade of people banging on pots and pans and singing roudy ballads—sometimes to force an unmarried couple to wed, sometimes to humiliate a man who couldn’t control his wife, sometimes in the case of older widows remarrying. It was a form of social control-- Hogarth made an illustration of this, which even at his time was becoming dated

As one historian puts it:

Both the state and the community relied on this collective opinion to ensure social order: hence the importance of one's 'good name and fme' in determining guilt and innocence in both civil and criminal trials/ the courts' use of 'shame' punishments - the pillory, stocks, cucking stool and public whipping - to solicit community participation in the public destruction of the reputations of those convicted of certain crimes

So, in result, there was a high amount of pressure on men to assert their manhood through sexual control of woman. When a man was single, it was more than okay for him to brag about his sexual conquests, but as soon as he became married, it became essential for him to control their wives to avoid the risk and danger of being called a cuckold. The humiliation of such an event could spell loss of respect, honor, and in some cases lead to duels or fights. There is much to say about history of masculinity here that /u/Georgy_k_Zhukov might want to say here that I don’t know as much about.

Regardless, this held more or less true through the 16th and 17th centuries. The difference is that by the 18th century, the amount of community control over sexuality had begun to collapse – partially because of the rise of a more professionalized and urban police force that was more concerned with enforcing very visible sorts of disorder such as drunkenness and fighting and partially because church courts, which were the arbitrators and enforcer of english morality for so long never managed to recover after the Civil War.

As Shoemaker puts it

As the individual ceased to be so closely watched by the community, estimations of honour and reputation became less publicly defined. Craig Muldrew has traced a similar decline in the social and moral significance of 'credit' (a public reputation for solvency) between the seventeenth and eighteenth centuries, as new financial institutions developed to guarantee financial transactions. As he suggests, these changes might usefully be interpreted as part of the same process that created the modern notion of the individual, whose identity is determined by the inner, 'true' self.

By the end of the 18th century, the French Revolution had resensitized the minds of English people to the fragility of “the great family of the public,” the very “privacy” of the marriage contract seemed to argue against the intrusions of public law. “Adultery ceased to be a part of the history of cuckoldry and became a domestic tragedy, less a matter for public scorn (though that was still there) and more a part of private pain.”

In the context of a private, personal pain, the image of the cuckolded husband and the community and group humiliation that came along with it began to fall apart. The shame was individual and within the family, and did not need to be reinforced or bestowed on an individual by a larger community.

However, cuckold as an insult did not die off completely everywhere in the English speaking world. In fact, the term remained in vogue, in particular places.

One of those places was the American South, where the danger of black men sleeping with white women remained a paramount bogeyman – and still does. As you might suspect, this lead to the fetish and a porn genre that has heavy ties to humiliation and racism. A cuckold video usually involves an impotent and humiliated white man watching as his wife sleeps with a larger more powerful black man or “BBC.”

Edit: removed something that was a bit too far over the current politics line :)

Sources:

Fashioning Adultery: Gender, Sex and Civility in England, 1660-1740 - - - David M Turner

The Secret History of Domesticity--Michael McKeon

The Family, Sex, and Marriage – Lawrence Stone

The Decline of the Public Insult In London – Robert Shoemaker