Matthew 19:9 and Divorce

Once it is admitted that porneia refers to incestuous or illegitimate marriage, there is no obstacle to admitting that "sending away" one's wife refers to divorce, as was common Jewish usage. (cf 1 Cor. 5:1)

A Catholic source on the matter:

http://biblicalstudies.org.uk/pdf/scripture/08-3_075.pdf

A Protestant source that goes through all the possible meanings:

http://www.logosapostolic.org/bible_study/RP2095-Divorce-Fornication-porneia.htm