I won't speculate about what it means, other than I suspect that the marriage had hit a wall as far as Todd was concerned, and he had decided to go his own way. This happens after three decades of concerted tumult and change. In addition, Todd and Sarah may have had some deep disagreements over their future together. So he pulled the plug on the marriage.
As to whether there was another man or woman involved, no one can say right now. The fact that none of the gossip sites seem to be reporting anything of that nature seems to indicate that something else broke that marriage up. Todd always seemed to me like a stand-up guy who valued the marriage, as did Governor Palin.
Only a month ago they were in Sturgis, SD, on a biker rally that had become and annual pilgrimage for both of them, and their marriage seemed quite stable. Shortly thereafter, he made the decision to go forward with the divorce. I suspect that this had been brewing for some time, and may have been mutually agreed on between the two of them.
As to what it portends politically for the Governor, we don't know. Palin is now single, and free from potential charges of cheating on her husband. These charges would have come at her any time she had decided to reenter elective politics, not only from the Democrats, but from Republican operatives allied with the Bush Family, Romney and others in the Beltway GOP. But she may have decided to return to politics and Todd may have decided that that wasn't for him.
I just think he got sick of his home being a reality show. He wanted his own life back. Celebrity comes with a high price.
Thanks for an interesting post; it does give one somethings to think about.