Original Intent
The reason Yahshua gave for allowing divorce was 'due to the hardness of their hearts.' It seems safe to say that this was the same reason polygamous relations were allowed, even though the kings were warned not to multiply their wives or else, Deut 17:17. They suffered the consequences of their actions.
Neither shall he multiply wives for himself, lest his heart turn away; nor shall he greatly multiply silver and gold for himself, Deut 17:17 NKJV.
Most notable was King Solomon who was led astray into their false worship,
As Solomon grew old, his wives turned his heart after other idols, and his heart was not fully devoted to Yahweh his Elohim, as the heart of David his father had been, 1 Kings 11:4-5 NIV.
Not only did he have wives, but he added 'foreign' wives to himself, which was forbidden in Deuteronomy chapter 7:3.
When Yahweh your Eolhim brings you into the land you are entering to possess and drives out before you many nations — the Hittites, Girgashites, Amorites, Canaanites, Perizzites, Hivites and Jebusites, seven nations larger and stronger than you — and when Yahweh your Elohim has delivered them over to you and you have defeated them, then you must destroy them totally. Make no treaty with them, and show them no mercy. Do not intermarry with them, Deut 7:1-3a NIV.
He may, however, have reasoned that was alright as long as they were from distant cities.
This is how you are to treat all the cities that are at a distance from you and do not belong to the nations nearby, Deut 20:15 NIV.
When you go to war against your enemies and Yahweh your Elohim delivers them into your hands and you take captives, if you notice among the captives a beautiful woman and are attracted to her, you may take her as your wife. Bring her into your home and have her shave her head, trim her nails and put aside the clothes she was wearing when captured. After she has lived in your house and mourned her father and mother for a full month, then you may go to her and be her husband and she shall be your wife. If you are not pleased with her, let her go wherever she wishes. You must not sell her or treat her as a slave, since you have dishonored her, Deut 21:10-14 NIV.
When Judah came back from being in captivity for 70 years in Babylon, they came to know that they had to put away their foreign wives and children under the leadership of Ezra, Ezra 10:3. He did not tell them they couldn't remarry, but did show them from the law that they couldn't be married to their 'foreign' wives.
Today, one would be hard-pressed to figure out if one is of pure Israelite stock. This is evidently part of the reason why the Apostle Paul said to us today not to divorce.
And unto the married I command, yet not I, but Yahweh, Let not the wife depart from her husband: But and if she depart, let her remain unmarried, or be reconciled to her husband: and let not the husband put away his wife. But to the rest speak I, not Yahweh: If any brother hath a wife that believeth not, and she be pleased to dwell with him, let him not put her away. And the woman which hath an husband that believeth not, and if he be pleased to dwell with her, let her not leave him, 1 Cor 7:10-13.
The original intent was to have strong family structures that work to build the foundations of society with Yahweh as the focal point. Paul was evidently for this as well.
Homosexual relations that were forbidden in the Old Testament and that were forbidden in the New, will also not be allowed in the coming Kingdom of Yahweh. It just is not part of the original intent or overall plan, but today you see it becoming more prevalent even though Yahweh calls such things an 'abomination.'
Do not lie with a man as one lies with a woman; that is detestable, Lev 18:22 NIV.
Homosexual unions today are not recognized as marriages by Yahweh since they do not constitute the original intent of a man and a woman.
For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh, Gen 2:24 NIV.
There are also other improper relations, such as Herod having his brother's wife.
For Herod himself had given orders to have John arrested, and he had him bound and put in prison. He did this becauseof Herodias, his brother Philip's wife, whom he had married. For John had been saying to Herod, 'It is not lawful for you to have your brother's wife,' Mark 6:17-19 NIV.
That particular situation was probably seen by John as an incestuous relationship. Incest was specifically forbidden in the law (torah), Lev 18:16; 20:21. It may also be that John the Immerser took the Shammai School's view as Yahshua did, Matt 19:3-9.