In the beginning, God created Adam and Eve. He did not create any other humans. If Adam were to divorce Eve, there would be no one for him to marry. He would be alone. The same obviously would go for Eve. Divorce was not even an option that God gave His first children.
The Hebrew word for “divorce” is “ker-ee-thooth” and it pretty much means “divorce”. Fairly simple. The first time it appears is in Deuteronomy 24:1.
When a man hath taken a wife, and married her, and it come to pass that she find no favour in his eyes, because he hath found some uncleanness in her: then let him write her a bill of divorcement, and give it in her hand, and send her out of his house.
The word uncleanness here is a fairly broad term. There are several things you could tie this to but the most obvious one would be sexual immorality. The Son of God Himself in Matthew 5:31 and 19:3-9 gave us some more insight on divorce. The main one being 19:8:
He saith unto them, Moses because of the hardness of your hearts suffered you to put away your wives: but from the beginning it was not so.
And I say unto you, Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and whoso marrieth her which is put away doth commit adultery.
Even Jesus said that from the beginning divorce was not an option. It wasn’t even a “thing”. There was no such thing as divorce. The word “suffer” here means to allow but it does not mean to approve. God may “suffer” you to divorce, but He does not approve of it. In fact, Jesus stated there is only one reason that a divorce is allowed, without committing adultery, and that is if your spouse has committed a sexual sin. Although many divorces can fall within this category, it is not the cause of every divorce.
Notice that in the beginning with just Adam and Eve, there was no way for either one to commit adultery. It is the only one of the Ten Commandments that Adam and Eve could not break. There was no one else. Just Adam and Eve.
In the end, divorce is always something that God does not approve of. He will allow it for one reason, and that reason is adultery. Any other reason to divorce just leads to more sin.