Well, yeah. But it used to carry a severe social stigma and, according to several articles, is far more widespread now. Thus, it is eating away at the fabric of the family.
Yes, it used to be that a man who was unfaithful to his wife in this country and left her and his children to be with some young floozy would be socially ostracized. His friends would abandon him, business associates would not trust him, no one would talk to him. Now he and the young slut will be invited to every dinner party and no one will say a censuring word because they don't want to be considered "judgmental." It used to be that a woman who was caught committing adultery would nine times out of ten lose her children to him. She was regarded as little more than a common whore. Now, once again, no one says anything to her because that would be judgmental. When there's no social stigma attached to an action people tend to engage in it more frequently. Let's note the example of aggressive homosexual proselytizing as well.
Nobody's saying (at least, I hope nobody's saying) that adultery should be prosecuted as a crime, the way it once was. But as a people we ought to stop worrying about hurting the adulterers' feelings by speaking out. It's possible that when the children who have been robbed of their homes by adultery grow up they won't be afraid to express their anger more openly, and adultery will become as reviled as it was in the old days.
We can always dream!
Depends on how recently you're referring to....
Historically, a man was almost expected to have a mistress, to 'tup' the house maids, to visit brothels etc. Higher class couples had lovers on the side, with the attitude that descretion was the key. Love and fidelity to second place to status and heirs. Every era, you read of a man's legitimate children and then there would be a listing of his bastards. (I think Robert the Bruce had 13!)
Even in this century, it was more of a 'nudge nudge wink wink' situation if it came out that a man had a girlfriend in the city (where he worked) and a wife in the suburbs. There were lots of 'romantic' comedies based on this premise....the one that pops into my head is "The Guide For the Married Man".
Which dovetails right into the playboys, the players, playas etc that is common now. The attitude being a man can't just be happy with 'one woman' in his life. (This isn't meant to be gender biased, because I know women do the same).
I agree, that in most communities, affairs that came to light were viewed negatively. That infidelity is THE biggest trust killer in a relationship. But it does seem to be very prevalent.