that's the thing, the definition of marriage has not meant the same thing for thousands of years. it use to include polygamy, still does in some parts of the world. marriages were business arrangements made by the parents, still are in some parts of the world. in Europe a thousand years ago, marriages were arranged by serfdom kings and bishops too.
your definition of marriage is only a few hundred years old.
I thought it was older than that.
Deuteronomy 17:14-19 (New International Version)
The King14 When you enter the land the LORD your God is giving you and have taken possession of it and settled in it, and you say, "Let us set a king over us like all the nations around us," 15 be sure to appoint over you the king the LORD your God chooses. He must be from among your own brothers. Do not place a foreigner over you, one who is not a brother Israelite. 16 The king, moreover, must not acquire great numbers of horses for himself or make the people return to Egypt to get more of them, for the LORD has told you, "You are not to go back that way again." 17
He must not take many wives, or his heart will be led astray. He must not accumulate large amounts of silver and gold.
1 Timothy 3:2Now the overseer must be above reproach, the
husband of but one wife, temperate, self-controlled, respectable, hospitable, able to teach,
1 Timothy 3:12A deacon must be the
husband of but one wife and must manage his children and his household well.
Titus 1:6An elder must be blameless, the
husband of but one wife, a man whose children believe and are not open to the charge of being wild and disobedient.