God takes no pains whatsoever to prove Himself to us in His word. The Bible always presupposes our knowledge of His existence, because every human being knows God exists, and is without excuse. ¹, ²
Similarly, ANRs between married couples are taken for granted in Scripture. When God designed the institution of marriage, along with sex, family, procreation, and nurturing, He knew all five would be interwoven, so I believe that’s why He doesn’t bother emphasizing ANR beyond the three verses that exhort or imply it.
1. Romans 1:18-32: “18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. 19 For what can be known about God is plain to them, because God has shown it to them. 20 For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. 21 For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened … 25 because they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever! Amen. ... 28 And since they did not see fit to acknowledge God, …They are … haters of God, … 32 Though they know God’s righteous decree …”