This webauthor has a gut feeling that more than one Christian husband has both desired and contemplated acquiring a part-time young-woman sex partner other than his primary wife who he considers his own concubine, and which concubine considers that husband her own husband.
For both that husband, and his concubine, engaging with or being engaged as a not-married harlot or mistress is out of the question, because that would constitute hellish-consequence fornication or adulterous immorality.
The reasons for wanting a concubine, and thus an additional woman in his life, for a Christian husband, are generally because of some sexually-related deficiency and inadequacy of his primary wife (e.g. increasing non-attractiveness or disabilities due to advancing age, not able or non willing to pose nude in various positions for his private digital-cam photo album, do clothed-to-nude private striptease dances for him alone, give him enough satisfying penis-sucking fellatio, etc.). It is the younger women with more-attractive faces and healthy, active, slender bodies who are eager for sensual gratification, that he finds appealing.
Along those lines, incidently, it is interesting to note that the Old Testament is somewhat more sexually explicit than the New Testament in terms of describing heterosexual activities. For example, though both Testaments use the word "naked," only the Old Testament applies that specifically in certain instances to women - but the New never does. The Old mentions a man "going in to" and "laying with" women - but the New never does.
As you observed above, this webauthor has gotten somewhat more explicit than both, although not graphic in the sense of showing images and pictures of such (which licentuous impurity - if done - would probably have caused defiling lust in you, the aroused reader......especially if you are a male).
Multiple-wives polygamy, and the desire to acquire a concubine or concubines is indeed found throughout especially the first half of the Old Testament [Genesis 4:19, 32:22, Judges 8:30, I Samuel 1:2, 27:3, 30:5, 30:18, II Samuel 2:2, I Chronicles 4:5, II Chronicles 24:3] both before the giving of the Mosaic law and after the giving of the Mosaic law - culminating in Solomon's 300 concubines along with his Ecclesiastical statement that many concubines are "man's delight" (Ecclesiastes 2:8). Both Abraham and David had concubines, and children produced with those (Genesis 25:6 and II Samuel 5:13). Rehoboam had even more concubines (II Chronicles 11:21) and the wise and just king Ahazuerus, king of Esther, apparently had concubines also (Esther 2:14). Observing that the Holy Spirit through His author Saint Paul merely restricted (or limited, depending upon your point of view) bishops and deacons being husband to more than one wife.....is telling (I Timothy 3:2, 3:12, Titus 1:6).
It is interesting to examine those cases of concubinage in the Old Testament, and speculate as to the motivations of why and how both husband and concubine(s) thereof felt about concubinage. It is particularly intriguing that God Himself never condemned patriarchal polygamy. [The Torah, or Pentateuch, even has a law for a man having two wives at once pertaining to inheritance apportionment for their offspring] (Deuteronomy 21:15).
It appears that, for patriarchs of the Old Testament such as Abraham, Jacob, Gideon, Elkanah, David, and Solomon, the driving force behind concubine acquisition was not entirely the same as for the women mentioned. Moreover, it is obvious that the desire for having children on the part of barren women involved in acquiring concubines for their husbands was a significant factor, as was the case with Sarai (Abram's wife) giving Abram her maid Hager (which mother of Arab-son Ishmael the angel of the LORD provided for in the desert) and Rachel (Jacob's second wife at the time he was already married to Leah) giving Jacob her maid. It is not Scripturally recorded whether Sarai and/or Rachel arranged nice church wedding ceremonies and receptions for their husbands to be married to those other women, but simply told them to "go into her" (so that they could have children by proxy using those concubines). Whether or not Abram and Jacob really wanted children is not known, but it is assumed that most men do not particularly relish the thought of childbirth and child-rearing expenses plus time involved being bothered by whining, crying, screaming, shrieking, rebellious and selfish infants and toddlers, besides all the worrysome and dangerous mischief they get into in their teen years.
For Christian husbands and concubines, abortion-homicide preventing all that is out of the question, and children are the logical consequence of sexual activities between a husband and concubine, with or without messy and inconvenient condoms or body-harming spermicides and pill contraceptives. One sexually-related thing (whether it be lips-kissing, breasts-and-buttocks fondling, taking off all the clothes to being barefoot nude together in the shower and the marriage bed, and more) logically leads to another, finally being fulfilled in "don't-stop-now" genital-insertions coitus.
One key word to describe family relations in some cases of concubinage and multiple wives in the Old Testament is: rivalry. Competitive jealousy-based rivalry. Not exactly peace on the home front, to say the least.
For modern Christian men, knowing not only the Old but the New Testament (the latter of which is not fairly described as sterile in its semantics, but certainly less sexually explicit), there are obstacles to overcome in actually acquiring acceptable concubines for part-time sexual use and pleasure.
For one thing, frigidly prudish yet lascivious secular feminist-sexist society misconstrues any additional woman married to an already married man "bigamy" (which it is not in the Biblical sense). It is polygamy to be sure, but not [illegal] "bigamy." Classic unlawful bigamy would be a woman having more than one husband at a time, and NO where in the entire Bible is that scenario ever suggested or implied as legitimate and actually done by anyone on record throughout Scripture.
However, present society does acknowledge the acceptability of "common-law marriage" in which the consentual mutually-agreed-to marriage to and with each other of both heterosexual partners is not licensed nor registered as such with the State. In that case, the civil government does not regard such common-law concubinage as fornication, adultery, or bigamy. Any [permanent, of course] concubinal arrangement between a man and woman should, for the sake of mutual trust and mutual chaste fidelity, be written up as a mutual hard-copy contract between themselves, rather than merely have a no-written-proof, change-one's-mind-at-any-time verbal word-of-mouth agreement. [By the way, for the sake of clarification, any sexual connection into any bodily opening between heterosexual partners is NEVER rightfully considered "sodomy" (being that sodomy only involves erotic same-gender bodily connections of whatever types]
A Christian husband would only accept a concubinal candidate who is a believing Christian, in accord with I Corinthians 7 and II Corinthians 6:14. A disbeliever would be non-acceptable. Moreover, the candidate must always be modestly dressed year-round (especially during warm days) as to hairstyle, armwear, legwear, and footwear when in general public view so he is never ashamed of her and can trust her whenever he might see her in public. She must be discreet and able to keep her concubinage secret as much as necessary, under various circumstances. She also must be willing to be her husband's second-class spouse - knowing not only that his sexual energy and capacity will mostly be directed to her husband's primary wife, but she herself will have to be content with partial or limited sexual connections with him, yet never consider herself deprived dealing with a largely-impotent older man (remember the case of Ruth in the Old Testament)....probably stopping short of what frequently results in pregnancy....yet still and always remain faithful to him only.
Such a concubinal candidate is hard - but not impossible - for a Christian husband to seek, find, and enjoy....and - I'm sure - such candidates do exist, sometimes closer than one thinks.