I think he should resign. I think *all* politicians should resign (regardless of party) in these types of situations. As a "leader" I look to politicians to make good, thoughtful decisions (in an ideal world). If these guys make such poor decisions in their personal lives and treat their wives this poorly, I don't think that they will necessarily make good decisions in their political lives or be able to represent their constituents well. Plus, they have way to much drama going on in real life to govern well. That's my opinion. If your personal life is a circus stay out of public policy!
ETA: Plus the lying about it really bugs me. If he lies about this, he'll lie about other things. I also have to give the big stinkeye to the blogger that stalked him for the info. THe accessibility of media has a dark side that hyper-partisan people are exploiting mercilessly.