Not only did the slimeball Gerry Studds not resign, but the moron people of MA re-elected him several times. This was not over friendly emails either. He admitted having sexual relations with underage men and he got away with it. The double standard is sickening, but not the least bit surprising. It's been like this for decades.
The two different standards of behavior arise naturally out of the two different constituencies. Republican voters tend to believe in traditional standards of decency, democratic voters tend to not believe in them -- so if a bill clinton type conducts himself like a dog in heat, votes and campaign contributions will rise. Conversely, if a Mark Foley type does likewise, his base of support will quickly abandon him. This is the political price of paying more than lip service to the question of character in public life and it's a practical advantage the democrats have over the Republicans.