In his third lecture on Rabbi Chalom Messas for Torah in Motion, Rabbi Marc B. Shapiro says:
[In 2006], Zvi Zohar in Israel, an expert in Sephardic halacah, just came out with a book on 20th Century Sephardic rabbis.
He wrote an article saying we need to bring back the institution of pilegesh (concubine aka live-in girlfriend).
The Rambam says this is forbidden but the Ramban and the Ravad and most of the medieval authorities permit this.
Today this is out of style. We don’t consider this proper. We don’t consider this moral. In the last 20 years, morality in the larger society has changed and people don’t see a problem with living together.
The Jewish view is not that these people are “living in sin.”
When people say that living together is immoral, I have a problem with it because the Ramban and the Ravad said it was permissible. To say it is immoral insults our great sages.
This Lubavitcher woman goes around to these public schools and encourages people to get married and says that living together is immoral. But according to Jewish law, there is no such thing as marriage for non-Jews. Living together is marriage.
The OU puts out this literature saying that sex is special but you can only do it within marriage. If you remove it from marriage, it’s dirty. Excuse me! The Ramban and the Ravad and many other gedolim think differently.
According to everyone, the king was permitted a concubine.
Do you invite them to the Shabbos table? In my opinion, why not?