Many years ago, when I was still a young Christian, I was briefly mentored by a neighbor in Makati who was an American missionary. He and his wife worked as church planters and authors in Asia under the supervision of a large Christian denomination. After a long time serving together as Christian missionaries, the wife confessed that she was not a Christian when they got married and became one only just recently. It's a kind of shock. But at least, it had a happy ending.
In the lives of thousands around the world, men and women live life in that most difficult of all relationships: life and marriage to a non-Christian. Some survive and manage better than others. For a lot, it was a long, hard road, even a disaster instead of a delight. Its truly hard to share a life with someone when you don't both love God, serve and obey Him. One's spiritual life is the most important part of a marriage relationship.
Biblically speaking, read the apostle Paul who exhorted Christians not to be "unequally yoked together with unbelievers." Read also Ezra who warned a lot of men on marrying "strange wives" because they dilute the faith. And they cause children and people to stray from God. Or even see the example of king Solomon. Despite his wisdom, he fell from faith and put up idols due to his wives, inviting God's anger.
What about this case? Enrico (not his real name) married a fellow church worker. After many years of marriage, the wife committed adultery and has been continuing the sin and living a non-Christian, worldly life since then. Did Enrico marry a non-Christian woman in the first place? He thought he married a Christian woman but now he's not sure. How does Enrico live life as a believer from here on with an unrepentant wrongdoer for a wife?