The information that we have in the Bible says that Paul wasn’t married when he wrote 1 Corinthians:
To the unmarried and the widows I say that it is good for them to remain single as I am. [1Cor. 7:8]
However, we don’t know with absolute certainty if Paul was married before or after this — although, Paul’s emphasis on remaining single would suggest that he didn’t marry after he wrote 1 Corinthians.
It’s sometimes suggested that Paul needed to be married to be a member of the party of the Pharisees. However, I cannot find any reliable sources that say it was a requirement for Pharisees to marry. There is better suggestion that a member of the Sanhedrin needed to be married (although, again, the sources aren’t the most primary),1 but we have no reason to believe that Paul, although advanced in Judaism (Gal. 1:14), was ever a member of the Sanhedrin. Thus these are no reasons to think that Paul was married prior to writing 1 Corinthians.
If (and it is a big, speculatory ‘if’) Paul was married prior to writing 1 Corinthians, then it is possible that his (hypothetical) marriage ended with a divorce (if it was a divorce before his conversion in Acts 9 then, under the Law, he could have divorced his wife [Deut. 24:1]; if it was after his conversion, then the divorce would have been for ‘sexual immortality’ [Mat. 19:9]). An equally possible suggestion in this hypothetical situation is that Paul’s (hypothetical) spouse could have died, leaving Paul a widower.
On the whole, however, it seems more likely that Paul never married.
1. Benjamin Willard Robinson, The Life of Paul (Chicago: Chicago University Press, 1918), p. 35: ‘There was a rule that no one could occupy the responsible position of member of the Sanhedrin unless he had been married and had a son‘. Perhaps tellingly, however, there is no mention in the Jewish Encyclopedia of marriage as a “qualification” for Sanhedrin membership (article ‘Sanhedrin’, particularly the section ‘Appointment and Promotion of Members’. Online [accessed 24/12/10]).