1 Corinthians 7:10-11, 15

To the married I give this command (not I, but the Lord): A wife must not separate from her husband. But if she does, she must remain unmarried or else be reconciled to her husband. And a husband must not divorce his wife.

But if the unbeliever leaves, let it be so. The brother or the sister is not bound in such circumstances; God has called us to live in peace.