The whole point of the 10 Commandments is to serve as a yardstick, an immutable standard , to measure our own grandiose notions of righteousness against God’s standard.
“There is none righteous; no, not one.” Romans 3:10.
The Law is to show us that we ALL need a Savior.
“I’m OK, and you are not so bad” tends to put us on cruise control with regard to our attitude toward our relationship with a holy God.
God has given marriage and the sexual relationship within as a magnificent blessing - if both receive it as from God. Rejection of this is spitting in God’s face, telling Him, “You do not really love me.”
Fornication and adultery tell God that we do not trust Him to provide for all of our needs (not necessarily all of our “wants”.)
What is the point of including the word adultery and not the others like fornication? Did God make a mistake or did Moses or did they jus run out of stone?