I don't actually find that in the statistics, but you may have some information on that. A series of them likely wouldn't qualify as much more than visitors, rather than cohabitors.
But these cohabiting males do not take the place of fathers, as the often violent testimony of the un-fathered children makes very clear.
Not the visitors, certainly. But it's hard to make the case that a single mother is better off without a cohabiting male in the house, simply because there are anecdotal cases of abuse resulting. But let's face it, in married homes, drugs, alcohol, and abuse are quite significant issues. As of 1998 there were 20 million children living in single parent homes. To suggest that a 2 parent household is worse because the couple are not married is simply not logical.
But that doesn't mean nothing else will weaken such ties further. In fact, we already know from the European experience that social sanction for gay marriage weakens marriage generally and leads to widespread cohabitation among heterosexuals, with all the attendant ills for the children of such unions (who are increasingly raised by the state).
Well, this topic is not about gay marriage, nor am I a proponent. But I simply do not believe that the legalization of same sex marriages in Belgium, Netherlands and Canada recently have materially impacted marriages in general which have been declining for years in Europe as has childbirth rates. If the 50-60 percent divorce rate hasn't been a significant blow to marriage, I doubt a few hundred gay marriages are going to make a difference. What about the countries that have not approved same sex marriage? Do you have any stats on declining marriage rates in them? It's important not to confuse correlation with causation. There are likely many causes of Europe's problems.
The same is true of social sanction for cohabitation. When shacking up becomes just as accepted an arrangement as marriage, marriage will be further weakened, illegitimacy will increase even more, as always, the losers will be the kids.
It is and has been acceptable in most states. I recall reading that studies have concluded that couples that live together for a while before marriage generally have longer marriages. As long as sex outside of marriage is not banned, cohabitation is by far the lesser evil than a single parent household.
I sense this is more of a moral issue than one of substance.
Gay "marriage" is likely both an effect and a cause of family deterioration. A society that valued families would never even consider sanctioning gay "marriage" in the first place, so you have to figure the family was already on the downward slide in Scandinavia. However, once sanctioned, the gay "unions" cheapen the family even more in people's eyes, especially impressionable young people. They no longer see marriage as a special bonding of opposite sexes to create and nurture children, but just a pairing of any two (or perhaps more, I think Holland recently "married" a man and two women somehow) people who sexually desire one another. Who needs marriage for that? And if kids aren't an important part of marriage, and they can't be if gays can "marry", then why marry at all?
Your recollection is faulty, and the fault is evidently not accidental. The standard liberal talking point on this subject actually makes more sense: Couples who don't cohabit before marriage have more stable marriages than couples who do because they are people more likely to take marriage seriously. Of course, society would be best off if many more couples were encouraged to take marriage seriously. At one time, our laws served to encourage that. They proscribed fornication as well as adultery and made divorce difficult to obtain. The results were clearly beneficial to children, but they made the aging adolescents of the Sexual Revolution sexually frustrated, so they junked them, one and all.
On that other marriage-related issue, your prejudices do lead you in the direction of the liberal talking points. The most informed writer today on the effects of gay marriage is Stanley Kurtz. Check out his analysis in the Weekly Standard. It is certainly not what I would want for our society.