Now lets say you with your girlfriemd/wife or boyfriend/husban for many years a good 5=10+ years and you suddenly found out that he or she was a cylon would you break up/get divorced? Or would you stay together?
If that person, like six had a plan of world domination throw over the government and plans to wipe out our race, I would be in the same situation as a Jew being with a fifth collum nazi, that would be a moral question. I don't think I could be with a person that was intent on destroying my race. There those out there like Baltar, who are blinded to this with a self centered notion, well at least I will survive because she loves me.
If you were with the sharon side of things, you deplore what your people are doing and want to set things right by turning on the side you represent, I would stay with that person and encourage them. But I would have to be damned sure that she was in earnist about it. You would have to live with the fact of "what if", even if you trusted that person completely, you would have that in the back of your head, especially in a crisis moment, if she lied about being a cylon, maybe she's lying about other things too. Second guessing and sitting on the fence dipping either way is a dangerous place to be. Your own human doubt could bring about the end of the relationship.
Even in Helo's face you can read the doubt sometimes. On Kobol for example, when Sharon pointed the gun initially at Adama, he said something to the effect of, Sharon, what are you doing?
Girls Rule BSG a close second:-)