Gregory the Dialogist

The eye also of the adulterer waiteth for the twilight, saying, No eye shall see me. And disguiseth his face. There is nothing to hinder but that this may be understood even after the latter, seeing that he who desires to commit adultery, seeks out the dark. But whereas it is a sentence uttered against Heretics, it is meet that this thing which is declared be understood in a mystical sense. Thus Paul says, For we are not as many that adulterate the word of God. …

Morals on the Book of Job, Book XVI ↗

Thomas Aquinas

He shows the same thing to be true for the adulterer saying, "The eye of the adulterer," who spies on the bed of another, "watches for the darkness," so that he cannot be caught, and so he says, "saying: No one will see me," that is, he watches in the dark so that he will not be seen by anyone. As if the cover of night were not enough for him, he employs still other methods of concealment, and so he says, "and he will cover his face," by changing his clothes in some way.

Commentary on Job ↗