The guy went to a Republican not a Democrat, is that because it is his Rep? Or does that mean that somehow the Democrats couldn’t be trusted because it is something that the Democrats (administration) are involved with?
I will make a guess at your question. Liberals could care less what Petraeus was doing or with whom so long as he could be counted upon to do what they required. From what I have read this affair has not been a 'secret' to the administration. And most likely Petraeus would have testified as if nothing was amiss until the whistle-blower let the Republicans in on the investigation.
Once the Republicans were told, there is no way Petraeus could go and testify at a hearing with the possibility that one of those Republicans might ask him about his affair. Petraeus had to go. Can you imagine what kind of tv it would make for a Republican to ask Petraeus, when did President Obama know about your affair?