Proverbs 5:15-23 “Drink water from your own cistern and running water from your own well. Should your springs be dispersed outside, your streams of water in the wide plazas? Let them be for yourself alone, and not for strangers with you. May your fountain be blessed, and may you rejoice in your wife you married in your youth— a loving doe, a graceful deer; may her breasts satisfy you at all times, may you be captivated by her love always. But why should you be captivated, my son, by an adulteress, and embrace the bosom of a different woman? For the ways of a person are in front of the LORD’s eyes, and the LORD weighs all that person’s paths. The wicked will be captured by his own iniquities, and he will be held by the cords of his own sin. He will die because there was no discipline; because of the greatness of his folly he will reel.”
Unfaithfulness is easy. Unfaithfulness is the default of the human heart. Even believers have their old nature that fights against their new nature (which is given by the Spirit of God). Faithfulness is hard. Faithfulness requires discipline! And we are to be faithful to our spouses. We need to discipline our minds and hearts to single minded devotion. We aren’t to cheat on them. We aren’t to turn them in for a new model when they get older. Instead, we are to rejoice with them as we grow old together, and not seek sexual or emotional satisfaction elsewhere.