How should a Christian respond if a spouse has had an affair?

from the old testament

• God clearly condemns unfaithfulness. In Old Testament Mosaic law, adultery was an offense punishable by death (Leviticus 20:10; Deuteronomy 22:22). Though believers are no longer under the civil requirements of the Mosaic Law (so shouldn't expect the death penalty for infidelity), the law reveals God's view of adultery.
• Since God "hates divorce" (Malachi 2:16 NKJV), the believer's response to a spouse's infidelity should be a heart ready to forgive. In fact, the book of Hosea uses the symbolism of an adulterous wife and the spouse who takes her back as a picture of God's forgiveness of His adulterous people. God modeled forgiveness for us. Infidelity could lead to divorce, but that should not be the immediate or most prominent response.
• The pain of betrayal in a marriage is piercing. We can bring our sorrows to God and pray for emotional healing. Psalm 34:18 says, "The Lord is near to the brokenhearted and saves the crushed in spirit" (cf. Psalm 147:3).
• The sin of adultery is not just a sin among people but is ultimately a sin against God (Psalm 51:4), violating the holiness He expects from His image-bearers. Though God forgives repentent sinners, that doesn't mean there are no consequences for that sin. For example, David and Bathsheba's adultery resulted in the death of their son (2 Samuel 12:19).

from the new testament

• Jesus specified adultery as the marital offense that could justify divorce (Matthew 5:32, 19:9). This doesn't mean divorce is required when a spouse commits adultery, especially since Jesus also says that looking at a woman lustfully is also adultery (Matthew 5:28). The point is that our actions must consider that we're all sinners who need forgiveness (Romans 3:23).
• As sinners, we confess our transgressions, repent, and God has promised to forgive us (1 John 1:9). That sets the model for forgiveness of an adulterous spouse. Jesus tells His disciples, "If your brother sins, rebuke him, and if he repents, forgive him" (Luke 17:3). Repentence is part of that process, something the unfaithful spouse should exhibit.
• Forgiveness doesn't mean that trust is automatically restored after infidelity, but the goal should be restoration. Even if the victimized spouse doesn't seek a divorce, he or she shouldn't wield past infidelity as a weapon in the marriage (1 Peter 3:9). Hebrews 12:15 warns, "See to it that no one fails to obtain the grace of God; that no 'root of bitterness' springs up and causes trouble, and by it many become defiled."

implications for today

Betrayal. It hits you when you hear a good friend gossip about you. You feel it when a friendly coworker takes credit for work you did. But no betrayal cuts as deeply as when a spouse is unfaithful. It seems impossible to recover from such a devastating wound. As Jesus said, though, "with God, all things are possible" (Matthew 19:26). While hanging on the cross, Jesus forgave even those who crucified Him (Luke 23:34).

But repairing the severed relationship may take time. Restoring a marriage isn't like restoring a house on HGTV shows. Trust, once lost, is more like "gut job" than a refresh. Church leadership may need to become involved. Believers can seek the counsel of their pastor or Christian counselor.

Even after all the work put in, divorce may be the end result after infidelity. Still, as believers, we are called to pursue restoration and seek reconciliation. This involves forgiving the person, putting them in God's hands, seeking their good. This may be hard, but forgiveness frees us from bitterness and allows God to be the judge of the situation. When there is no repentance or repeated sinful behaviors continue such as lying, cheating, or ongoing unfaithfulness, separation or divorce may be necessary, not as a failure of faith but as a sober acknowledgment of broken trust and unrepentant sin (Matthew 19:9; Hebrews 12:15). Even then, we are called to walk forward without bitterness, entrusting justice to God and healing to His care.

Praise God that He is near to the brokenhearted and that His love endures forever. God knows our hearts, and He alone can provide the healing we need to respond to a spouse who has had an affair. Betrayal will either shape us into people marked by bitterness or people marked by grace—so the real question is: will we let our pain define us, or let God transform it?