This may sound like a strange question, but it’s not as crazy as one might think. In the book of Genesis, figures such Abraham, Lamech, Esau, and Jacob had multiple wives (http://www.biblicalpolygamy.com/polygamists/). Now you might be saying:
I thought that polygamy wasn’t allowed? Well, you wouldn’t be alone in that thinking. I myself was always taught that it went against everything that the Bible says. However, many appearances of polygamy appeared in Genesis. In Genesis 4:19, as it is written in the Literary Study Bible (by Leland and Philip Ryken), “And Lamech took two wives. The name of the one was Adah, and the name of the other Zillah.” In Genesis 16:3, Sarah, Abraham’s wife, gives Hagar, her servant, to Abraham as a wife to produce children because Sarah believed she would never have children of her own. Also, in Genesis 26:34, we see Esau take two wives. The text says, “When Esau was forty years old, he took Judith the daughter of Beeri the Hittite to be his wife, and Basemath the daughter of Elon the Hittite, and they made life bitter for Isaac and Rebekah.” (Literary Study Bible) Esau would later take a third wife, Mahalath, in chapter 28 (http://www.biblicalpolygamy.com/polygamists/esau/). Finally we see Jacob take four wives in Genesis chapters 29 and 30 (http://www.biblicalpolygamy.com/polygamists/jacob/).
We also see concubines with Abraham. A concubine, just for a clearer understanding, is a concubine is a female who voluntarily enslaves and sells herself to a man primarily for his sexual pleasure (http://www.gotquestions.org/concubine-concubines.html). In Genesis 25:6, just before his death, Abraham gives gifts to the sons of his concubines (Literary Study Bible).
With all of this, you might think that polygamy and adultery are:
Well, in a word:
While it is true that these things did happen, that doesn’t exactly mean they they were allowed. While the book of Genesis never shows God outwardly condemning these actions, it also never says that he approved of it either. Therefore, we have to look deeper. The first man to take multiple wives, Lamech, was a godless man. While these patriarchs have practiced polygamy/adultery, never once was it to honor God. Also, the results of these actions never once ended well. (http://theresurgence.com/2009/11/02/is-polygamy-biblical) As a matter of fact, one might could argue that the results of these actions could count as a curse from God. The case of the love triangle between Abraham, Sarah, and Hagar could be a great example of this.
“God promised that Hagar’s son, Ishmael, would become the father of a great nation because he was a son of Abram, though not the son of the promise (which would eventually be Isaac). God promised that Ishmael would be a “wild donkey of a man” and that he would be a warrior in hostility with his brothers who would descend from Abram. Ishmael was born to a Hebrew father and Egyptian mother and became the father of the Arab nations that to this day are in hostility with Jews and Christians alike, as promised.” (http://theresurgence.com/2009/11/02/is-polygamy-biblical)
Let’s not forget that it wasn’t until after the fall of Adam and Eve into sin (Gen. 4:23) that polygamy occurs. (http://www.letusreason.org/Biblexp185.htm)
In conclusion, while the patriarchs of the book of Genesis did practice adultery/polygamy, it doesn’t mean that it was right in the eyes of God. Later on in the New Testament, the Bible makes it clear that He intends marriage to be between one man and one woman—as it was “from the beginning” (Matthew 19:8; Mark 10:6). (https://answersingenesis.org/family/marriage/what-about-polygamy-in-the-bible/)
This just goes to show that: