Matthew 5:31-32 (NIV)
Divorce
31 “It has been said, ‘Anyone who divorces his wife must give her a certificate of divorce.
32 But I tell you that anyone who divorces his wife, except for sexual immorality, makes her the victim of adultery, and anyone who marries a divorced woman commits adultery.
Did you notice the Greek word was for adultery is in the passage, and not for the exception ? Adultery is specified as the result of divorce and remarriage, not as a valid excuse to do it. Adultery is not fornication (porneia).