The only other biblical grounds for divorce that I find in the Bible pertain to a divorce that an unbeliever seeks because he (or she) does not wish to live with a Christian spouse. I understand Paul to be instructing Christians not to divorce.
If they have already divorced, the must either remain single, or they can only re-marry each other.
While Jesus looked upon divorce as a "necessary evil" for those who live in a fallen world, it is never looked upon as good.
It seems to me that those who hold to this highly restrictive view fail to remember the purpose of divorce.
Divorce was permitted because of man's sin; it was a protection for the innocent party.
They would turn to texts like Matthew , to prove their point.
I would agree that the engagement was taken so seriously it had to be broken as though it were a marriage.
I disagree that this limits our Lord's words to the engagement period, and not beyond.