Certainly, the answer is found in response to the following questions.
Who was the audience that directly ask the question and to whom Jesus directly answered?
What was the marriage custom of that day?
In the custom of the Jews, was there a time when one was considered married and yet not "one flesh?"
Look at the statement by Christ:
"For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh, so they are no longer two, but one flesh. What therefore God has joined together, let no man separate.”
Some would take the statement of Christ, "I say to you, whoever divorces his wife, except for immorality, and marries another woman commits adultery,” to be the "exception" to make divorce "legal."
Such thinking, in effect, states that something man does can undo that which God joined (Henry VIII thinking). However, there is no place in Scripture where such authority is given to human kind. God is never subjected to humans.
On a side, there is great information as to the thinking of Henry VIII:
HERE
When is the ONLY time that one (in the Jewish culture of that time) was married but not "one flesh?" During the time we might call "engagement" although in the Jewish custom of the day, the marriage ceremony had already taken place, the bride was merely waiting with the bride maids on the groom's coming to take her away.
There is also that which Paul stated concerning those who became believers, yet the partner did not. If the partner divorced them, they were not to remarry.
"But to the married I give instructions, not I, but the Lord, that the wife should not leave her husband (but if she does leave, she must remain unmarried, or else be reconciled to her husband), and that the husband should not divorce his wife."
See, this is the Lord's instruction, not Paul's.
Paul is restating what the Lord taught.
Now just beyond is the condition if the unbeliever divorces in which Paul indicates this is his view and not a directive from Christ:
"...if any brother has a wife who is an unbeliever, and she consents to live with him, he must not divorce her. And a woman who has an unbelieving husband, and he consents to live with her, she must not send her husband away. ... Yet if the unbelieving one leaves, let him leave; the brother or the sister is not under bondage in such
cases, but God has called us to peace."
The "not under bondage" is not referring the person is free to marry another. Rather it is referring back to the earlier part of the discussion having to do with the physical body belonging to each other.
Hope this helps the readers understand.
I realize that this post is counter culture, and typical modern believers are not taught this standard, but given a "home free" as if marriage is merely a game in which someone can merely walk away. It is also NOT seeing the marriage as a covenant, but as that of one making a vow to God. Covenant marriages are conditional, but those based upon vows are not dependent upon the actions of the partner.
