Jesus taught that if a man would divorce his wife and marry another, he would commit adultery. In other words, He taught in the following passages that divorcing one’s wife plus marrying another results in adultery (all NKJV, emphasis added):
"And I say to you, whoever divorces his wife, except for sexual immorality, and marries another, commits adultery; and whoever marries her who is divorced commits adultery." (Matt. 19:9)
So He said to them, "Whoever divorces his wife and marries another commits adultery against her. And if a woman divorces her husband and marries another, she commits adultery." (Mark 10:11-12)
"Whoever divorces his wife and marries another commits adultery; and whoever marries her who is divorced from her husband commits adultery." (Luke 16:18)
I take these passages to mean that such divorces are not recognized by God and, thus, when the man takes a second wife, he’s still married to the first wife, therefore being guilty of adultery (i.e., cheating on his first spouse). It appears Jesus’ stance assumes a man can only be married to one wife such that relations with another woman is tantamount to adultery even if he divorces the first wife ("except for sexual immorality" according to Matthew’s account) and marries the second. But if taking a second spouse can result in adultery even after divorcing the first spouse and marrying the second, then wouldn’t the same also be the case if the man didn’t divorce his first wife when he married a second one?
Is my understanding of Jesus’ teaching in these passages correct? If so, then wouldn’t His teaching imply that when married to a wife, a man can’t then marry a second wife (i.e., polygamy) without committing adultery against the first wife? If these passages don’t implicitly condemn polygamy, then how can a man divorcing his wife and marrying another be called "adultery"?
Appended Bounty Question
What exactly is it that makes a man’s divorce and subsequent remarriage "adultery"? Is it 1) the divorce, 2) the marriage to the second wife, or 3) both? If it’s option 3, then how exactly does the husband’s marriage to the second wife "commit adultery" against the first wife, considering that the first wife already lost her husband regardless? If it’s instead option 1 (the divorce), then is divorce by itself adultery? Why does Jesus also add remarriage? If, instead, we say it’s option 2, then would polygamy be condemned as adulterous? Jesus’ mention of divorce would therefore be because divorce is the contextual subject matter under discussion. Jesus would be saying that the divorce isn’t recognized by God, so divorcing wife one doesn’t free the man to marry someone else. What is the accurate interpretation of why the man’s action "commits adultery"?