THE NEW CATHOLIC ENCYCLOPEDIA SAYS THIS ON DIVORCE

Jesus when asked if divorce was allowed said that God's plan is strictly one man and woman for life meaning that divorcing and remarrying is adultery.  Only in the Matthew gospel does he say that unfaithfulness or porniea is a separate case, "except for unfaithfulness or porniea".  Some read too much into this and say divorce is permitted for adultery.

The New Catholic Encyclopedia, DIVORCE (IN THE BIBLE) says that Matthew 19 where it says except for porniea just allows separation without remarriage or that it is on about concubinage or fake marriage so a divorce that is not a real divorce is allowed in cases of adultery.

If it allows separation without remarriage on the grounds of adultery then something interesting happens if you consider Jesus’ declaration that divorce for any reason but adultery is making the divorced commit adultery.  Then the texts are saying that to divorce someone except for adultery is to make them commit adultery for it is certain once they are out the door they will make plans to get somebody else to have sex with and perhaps wed.

If Jesus only allowed the divorcing in invalid marriages, he would mean that if somebody commits adultery their spouse can have the marriage checked out to see if it was real and if it was unreal they can get a civil divorce and remarry. But otherwise the marriage should be assumed to be real despite all appearances. Therefore to use this procedure for any other reason would be making the spouse commit adultery.

Then the third possibility is stated by the encyclopedia to be that the exception does not refer to the verb for put away but to something else. It may refer to the question Jesus was asked about what the Law of Moses meant when it said a man could separate from his wife because of some indecency in her. So by saying porniea is an exception, Jesus meant that porniea or indecency was an exception not for divorce or remarriage but that he was not going to discuss its meaning. So what he meant was divorce and remarriage are always wrong but indecency was to be left out and to be an exception from the discussion. In support of this theory it can be argued that the word porniea is very ambivalent and unclear.

Clearly then he was saying he will not make it in anyway complicated.   It is a no to divorce and it is that simple.