(This is an archived correspondence at The Path of Truth. We have sent notification to the correspondent.)
The practice of husbands and wives SLEEPING in the same bed or in the same room seems to come from that the vast majority of people lived in houses or dwelling units that had only one room. Voiding was done into a common latrine away from the houses.
The wealthy, on the other hand, lived in large houses of several rooms. Husbands and wives could have separate rooms. Wealthy couples also usually had servants, and it was acceptable and proper for wives to send their maidservants as concubines to their husbands when the wife was menstruating, purifying, pregnant or just out of sorts. Many wealthy men had two or more wives. Whichever one was available shared the husband's bed for sexual relations while the other menstruated, was in purification or was pregnant.
If a wife did not desire to be pregnant, she might avoid sexual intercourse during her fertile days. It is not correct that "NFP" was unknown to the ancients. They probably did not know the biology but they did know of the infertile and the fertile days of the woman's cycle. The Manichees and the Cathars were condemned by the Catholic Church for practicing "NFP." They were accused of using their wives as harlots solely for pleasure, not being open to procreation.
The use of maidservants, concubines and multiple wives gradually passed from common acceptance after Constantine I established the "Catholic" Church as the official government religious organization of the Roman Empire. Ancient Roman law forbade bigamy in the interest of simplicity of inheritance. With the merging of the Catholic Church and the Roman state, church law and civil law merged also. No longer was bigamy to be accepted by what had once been the Christian church. Concubinage was legal, though, because the children of concubines and serving maids did not inherit their father's name or share in his estate unless he adopted favored ones. They were not bastards, for their parents' relationship was legal.
The Catholic Church, though, pressed its members not to practice concubinage. Bigamy was already illegal according to canon/state law. However, concubinage continued to be practiced especially in outlying regions. Clergymen were forbidden repeatedly not to have concubines, demonstrating that the practice persisted. Priests and monks continued to beget children from nuns without the formality of taking them as concubines. This was condemned over and over.
Remember the sitcoms and movies of the 40s and 50s? In bedroom scenes the husband and wife slept in twin beds separated by a night table. He wore full long sleeved and long legged pajamas and she wore an opaque nightgown.