I can't speak for Newt Gingrich's current marriage or the prior two. But I'd like to surmise why the 2nd Mrs. Gingrich is speaking out.
I think it's akin to what happen to Herman Cain during his campaign, at the beginning he was popular, but no where near being the nominee. But as his success grew, the people he had worked with grew more concerned. Because of his past behavior with them, they didn't believe he wasn't worthy of being the Republican nominee. So theses women spoke out, even when inevitably they were described as a woman scorned or accused of looking for a payout. In the end the pressure was too much, and Herman Cain called it a day.
Perhaps Marianne Gingrich, thinks it best to speak out now, before the Republicans chose a conservative in sheep's clothing.
I still believe Mitt Romney will be the Republican nominee for President. Gingrich has too much baggage and Santorum tries to be more Catholic then the Pope.
And I don't know about you, but just like Billy Joel sings "I'd rather laugh with the sinners, then cry with saints. The sinners are much more fun..."