Have you not read that he who created them from the beginning made them male and female, 5and said,(
H) 'Therefore a man shall leave his father and his mother and hold fast to his wife, and(
I) the two shall become one flesh'? 6So they are no longer two but one flesh.(
J) What therefore God has joined together, let not man separate."
Here is the record of the very first marriage as ordained by God!
22And the rib that the LORD God had taken from the man he made[
h] into a woman and brought her to the man. 23Then the man said,
"This at last is(
V) bone of my bones
and flesh of my flesh;
she shall be called Woman,
because she was(
W) taken out of Man."[
i]
24(
X) Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh. 25And the man and his wife were both naked and were not ashamed.
Next one....
16Then Cain went away from the presence of the LORD and settled in the land of Nod,[
f] east of Eden.
17Cain knew his wife, and she conceived and bore Enoch.
So how did Cain have a wife without the law telling him so?
There are a lot of instances where the man 'knew' their wives (slept) and they became one flesh. No law came between their covenant.
You said, yourself that the law was only recent...and after that the law was then added to come between a man and a women and their covenant before God.