The laws of Yahweh God must
first be understood within the context of the patriarchal society, before we can even begin to imagine how to keep them in the liberal feminist society of today. And it is impossible for us to keep them all, because we have no power to enforce many of them while we are in captivity.
The Harlequin Romance concept of marriage is to a great degree a product of more recent liberal feminist society. In the ancient patriarchal society, marriage was arranged between a man and the father of his prospective wife, and the woman often did not have a say in the matter. Such was the case with Leah.
But then there are also the cases of Hagar, Bilhah and Zilpah, and neither did any of them have a choice. They were all slaves who were married unto either Abraham or Jacob. Now, in the ancient world a concubine had a lesser legal status than a wife, but they were wives nonetheless, and a man would be punished for violating the concubine of another.
2 And Jacob's anger was kindled against Rachel: and he said, Am I in God's stead, who hath withheld from thee the fruit of the womb? 3 And she said, Behold my maid Bilhah, go in unto her; and she shall bear upon my knees, that I may also have children by her. 4 And she gave him Bilhah her handmaid to wife: and Jacob went in unto her.... 9 When Leah saw that she had left bearing, she took Zilpah her maid, and gave her Jacob to wife.
So the real dynamic governing marriage in the Old Testament is property rights. The father, or male next-of-kin, had property rights over his daughter(s). A man had to satisfy the father, not necessarily his daughter, to have her in marriage. So it was again, with Rebecca, Rachel and Leah. So a man's commitment to the marriage transcends his commitment to the wife, as it would extend to the family of the wife.
As for the idea that a marriage must have two witnesses, I must ask this: If a man were convicted of murder, must the two witnesses have been there as the murder took place, and also agreeing to the murder in advance of the actual act? In the ancient world, the parents of the woman and whatever other family were present would be witnesses enough to the fact of the marriage.
Therefore the witnesses to a marriage may surely be after the fact. If I tell my companions that I married a woman, that she was living with me as my wife, and they observed that woman or she was there consenting to my words, then each of my companions becomes a witness to my marriage. If I do wrong to my wife, or they find her with another man, then all of my companions can attest to the damage done. That is why we need witnesses.
Betrothal is the securing of a wife by promise or contract until the act of consummation. The man has a promise of marriage, and the law recognizes such a promise and gives the man certain protections in expectation of its fulfillment. It is not exactly equivalent to engagement, since the woman herself need not be a part of the contract. Many circumstances, such as the preparation of a home or the need for time to fulfill certain requirements set down by the father, could result in an extended period of betrothal. Because of the treachery of Laban, Jacob was betrothed to Rachel for fourteen years.
But Jacob was never betrothed to Leah. So betrothal is not a necessary step to marriage.
This is the context, in part, in which the laws in Deuteronomy must be understood.