1 Corinthians 7:10-11, 15

But to the married [believers] I give instructions—not I, but the Lord—that the wife is not to separate from her husband, (but even if she does leave him, let her remain single or else be reconciled to her husband) and that the husband should not leave his wife.

But if the unbelieving partner leaves, let him leave. In such cases the [remaining] brother or sister is not [spiritually or morally] bound. But God has called us to peace.