Righteousness and justice are the foundation of your throne;
    love and faithfulness go before you.

-Psalm 89:14, NIV

I believe adultery is affront to the very throne or authority of God.

As the Psalmist states here, we see love and faithfulness as linked to the symbol of God’s authority–i.e. His throne. Adultery is the opposite of love and fidelity–aka faithfulness. Hence, it is an affront to the very throne of God.

Adultery is sin…

…so, it is UN-righteousness.

Adultery is stolen intimacy (and often other marriage resources)…

…so, it is unjust.

Adultery is rightfully called evil in the Bible (see Deuteronomy 22:22). It is a sin that is an assault against God’s authority. In multiple ways, the adulterous spouse is defying God through their chosen sin. It is truly, truly wicked.