Thanks for all of your kind words. After I slept on it, I decided to practice love, acceptance, and compassion. My sister is scared for me (although has no reason to be) and feeling guilt and shame herself for her own affairs. There is likely envy too, since she skulks around to have other loves, I can do it right out in the open. My marriage is happy and better than it has ever been. And thanks especially Redpepper, I do very much believe that as time passes, and she sees my happiness, it will become less of an issue.
My sister is bright, inquisitive, and opinionated. So...she will not likely ever admit she was wrong, but it will be evident in time. In a way, I think I need to not "expect" people to automatically accept. It would be like going to a conservative Christian fundamentalist (no offense to anyone, I used to be one) and expecting them to just accept at face value. While she is not a conservative Christian, she is clearly a monogamist.
What are the best resources for reading that you would give to a family member?