lexical,
I'm sorry this happened. I would suspect that when it comes to people finding out something private about us, this is the worst.
At this point, since two people do know the truth, you can't go back on it. I would focus on minimizing it. I don't think you should make an announcement, as everyone is bound to hear about it in quick fashion. I would say just present as nonplussed about it (as someone else said on this thread). Say, "yes", if someone asks and then brush it off before they can ask a lot of questions. It is something about your past, sure, but if you act like it is no big deal, they will feel like idiots if they do.
I don't even think you should feel like you have to go your boss with it. If he asks, do like you did with the others, say yes and move on. If you look at people like it is strange that they think it is a big deal it will
1) Shift their thinking to it not being a big deal
2) Make them feel like a douche for seeing it as a big deal
Hang in there, it will wash over the workplace and then things will get back to smooth sailing. Just hang in there until it is over. Tough to do, I know.