No. God never excuses affairs in any marriage. Jesus taught, “But from the beginning of the creation, God made them male and female…and the two shall become one flesh; so then they are no longer two, but one flesh. Therefore what God has joined together, let not man separate.” Mark 10:6-9 (NKJV)

Your spouse is breaking the marriage vows against you and against God. It is adultery. All marriages have ups and downs. Both partners need to humble themselves and change their ways. If we recognize marriage trials as disciplines from God, we will develop our characters.  Hebrews 12:7, 11 (CSB), “Endure suffering as discipline: God is dealing with you as sons…No discipline seems enjoyable at the time, but painful. Later on, however, it yields the peaceful fruit of righteousness to those who have been trained by it.” That training changes our hearts and behaviors.

Jesus taught that anyone who divorces does so because of a hard heart. That spouse has not grown and matured through the conflict. Instead, that person has hardened their heart. Mark 10:2, 4-5, “The Pharisees came and asked Him, ‘Is it lawful for a man to divorce his wife?’ testing Him… They said, ‘Moses permitted a man to write a certificate of divorce, and to dismiss her.’ 5 And Jesus answered and said to them, ‘Because of the hardness of your heart he wrote you this precept.’”

Finally, whoever divorces their spouse and then remarries commits adultery. Mark 10:11-12, “So He (Jesus) said to them, ‘Whoever divorces his wife and marries another commits adultery against her. And if a woman divorces her husband and marries another, she commits adultery.’”

When adultery wounds a marriage, that couple requires marriage counseling. It would be wise to go to a Christian marriage counselor to repair the marriage. Sometimes only one spouse is willing to enter counseling. That person should go by himself or herself. A marriage is a close partnership. Both people are interacting according to established patterns. But if one person starts talking and acting differently, the spouse reacts to the changed behavior. Old patterns begin to break apart. 

The spouse may or may not choose to repent and grow. But what the spouse chooses to do is his or her responsibility. You cannot force your spouse to change. 

Marital change is painful. It takes a long time. So, be comforted by the Apostle Paul's words in 2 Corinthians 12:9 (NIV): “But He (God) said to me, ‘My grace is sufficient for you, for my power is made perfect in weakness.’ Therefore I will boast all the more gladly about my weaknesses, so that Christ's power may rest on me.” God will help you.