Within marriage, such thoughts aren’t necessarily “impure” or sinful. God created sex and our ability to feel pleasure. Consider Psalm 16:11, for example. He’s okay with our getting a mild buzz from booze (Psalm 104:14-15), but warns against drunkenness (Ephesians 5:18, among many others). But consider Proverbs 5:15-20—the last verse providing the context for Hebrews 13:4. (In fact, have a look at the Song of Songs/Solomon sometime. God isn’t a prude.) God encourages us to get completely blitzed with our spouse’s delights.
So, does this mean that all’s fair in marriage? Not quite. Spousal r@pe is a thing. It’s always sinful to treat someone made in the image of God as a mere tool for our own desires. The proper attitude is not, “I want to use you,” but “I love you and want to bless you.”
Upwind or downwind?