Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?
2 Corinthians 6:14
Doesn’t sound like this applies to the couple under consideration. Apprently neither has come to looking at things from God’s point of view. Both need to see that each is walking the path that leads to eternal pain and loneliness, not as children of God.