1 Corinthians 7:16

For what knowest thou, O wife, whether thou shalt save thy husband? or how knowest thou, O man, whether thou shalt save thy wife? (KJV)

Then: Christ first. Not my will but his. That's the goal no matter the action of the believer. It could be his or her influence will convict an unbelieving spouse whether it be through the daily life of marriage or the amenable actions of a peaceful separation. Thiselton (p. 537-538) presents the commentators discussion of a "pessimistic" translation. In it, the text actually refers to going ahead to divorce solely because the believer has no real basis to hope that his/her actions within the marriage will ever bring the unbeliever to salvation.

Now: For a long time murderers and thieves had a better chance of being forgiven and accepted into the life of the church than someone who had been divorced. The first group had many biblical cohorts - Jacob, Moses, and Paul himself were notorious for their actions and admirable as reformed people. They were leaders. But divorced people are shunted aside and not welcome to do anything but sit in the back pew. Sometimes exceptions were made, at least when the innocence of a particular individul was well known. As society is filled with more and more divorces, however, attitudes are changing. More forgiveness is proffered and greater space is found for them to serve within church ministries.

Extra source: The First Epistle to the Corinthians: a commentary on the Greek text by Anthony C. Thiselton (Authentic Media, c2000) online at http://books.google.com/books?id=IHG_DNLpmroC&dq=1st+Corinthian+commentaries&printsec=frontcover&source=in&hl=en&ei=W9fQSpC1GILplAfHiumoCg&sa=X&oi=book_result&ct=result&resnum=11&ved=0CB8Q6AEwCg#v=onepage&q=&f=false