If you are someone who thinks a politician's personal life, ethics and choices have an impact on their ability to effectively lead, then you CANNOT SERIOUSLY consider supporting one, Newt Gingrich - regardless of how much you agree with his political ideas.
And this is not just because you would be contradicting yourself by supporting the Newt, but also because, well, Newt has proven to be an opportunistic hypocrit on top of a being a cheater. After all, this is a man who led efforts to impeach a president for extra-marital relations while himself having extra-mariatal relations who now justifies his own problems as he was so busy that his judgement was impared. Wow.
Personally, I don't think a poiticians personal indiscretions (as long as they are of course legal and conentual!) are a major factor in determining if he or she will be an effective leader. But, I think someone who literally adopts a holier than thow approach on these matters, is exposed as doing the very thing themselves and then tries to brush it off and justify their own problems away is very unqualified for office. I also think anyone who does this and invokes "God" such as Newt is doing exposes them even further as desperate and untrustworthy.
I also think that this situation is one of those things where the people most aggressive against social issues (fidelity or homosexuality for example) often times are operating so aggressively to cover up or make themselves feel better about thier own situation. Show me someone who hates gays, I'll show you someone who is probably gay. Show me someone infuriated about extra-martial affairs, I'll show you someone who probably has had an extra-martial affair. Like that.