The verse that you have asked about was translated as unfaithfulness or Adultery by Protestant translators in the 16th Century. The original Greek word is Pornia, which when the Gospel was written did not mean unfailfulness after marriage, but to one’s fitness to marry prior to ones vows. So a woman (or man) who had fornicated, or had sexual relationships before marriage would not be able to enter into the sacrament without disclosing it to the spouse before the marriage, and having the Bishop absolve the impedement.

For Henry VIII and other Protestants the change allowed for a radical change, including demoting Marriage from being a Sacrament to a simple legal contract, with little or no Graces. An oversimplification, but it has boiled down to this in practical terms.