I was wondering if you could help me with the following: How would you respond to a man who was married, and after four years of marriage his wife committed adultrey. He decided to move out. The two remained legally married for another whopping 8 years, but both ended up living with other people and sleeping with other people during that 8 year span. Finally, after 8 years the wife finally legally divorced him to marry another man. Now the man thinks he can remarry because she commited adultery against him and the marriage was over in his mind; however, he did not put her away and sexually betrayed the marriage as well. How would you respond to this?
Both were involved in continuing adultery. What Jesus talked about in Matthew 19:9 is when one spouse is involved in fornication and the other is not. Therefore applying Matthew 19:9 to this situation is not possible.
His claim that he imagined divorcing his wife is false. Divorces are not personal whims. However you slice it, he has been living a sin-filled life for the last eight years.
I don't see any justification for a second marriage, but I see that repentance from sin is needed.