I Corinthians 7

15 But if the unbelieving depart, let him depart. A brother or a sister is not under bondage in such cases: but God hath called us to peace. 1
The unbelieving man or woman married to a Christian can depart at his or her own will even though the Christian does not desire it. It is always better for the couple to remain married. Nevertheless, the Christian does not have to go to unnecessary lengths to keep the partner. Let him or her go.
However, the decision is critical as to remaining single if that is the choice. Abstinence is required (v.11).

Next verse, previous verse, other verses

1The Holy Bible: King James Version. (1995). (electronic ed. of the 1769 edition of the 1611 Authorized Version., 1 Co 7:15). Bellingham WA: Logos Research Systems, Inc.