“Now for the matters you wrote about: “It is good for a man not to have sexual relations with a woman.” (1 Corinthians 7:1)
But if can’t
“But since sexual immorality is occurring, each man should have sexual relations with his own wife, and each woman with her own husband.” (1 Corinthians 7:2)— note the ‘singulars’ used here proving, “one man-one wife” relation Biblically according to God’s Will.
The stories of the ancient Jewish patriarchs having more than one wife proves that they did it contrary to God’s perfect principle but He tolerated it in His Mercy.
So, fact is, His Principle (which is Perfect) doesn’t change .