Ok, Card, I am a straight shooter so here are my thoughts. Please take them with the mindset that I care about you.
As far as facebook..Im thinking that if there are out of town friends who you havent been close to in 2 or 3 years and they arent in touch with you to know, I wouldnt be worried about them.
For me, the people who mattered in my life, knew what was going on as much as I told them. Anyone else, would find out when they did.
I dont really like having my life play out on FB, but, that's just me.
I think you want to set the record straight.
So, here's my question to you. Who does Card want to be?
As far as your sister's friend. I am confused. You were pretty raw the other day about your marriage.
In fairness to yourself and to anyone else, you need to finish your stuff, mourn the end of your marriage and figure yourself out before you should even think about another relationship.
I feel that people should be alone in order to do that. Be good with yourself. Find happiness within. People should enhance our joy not define it.
Something else to think about. If you do eventually see this woman..every argument, everything that happens within the relationship, could potentially be shared with your sister and effect the friendship in some way.
Card, get through this. Find you. Let your life unfold as it is supposed to. Plenty of time for all of that.
It matters that you stood. It matters that you become your best self.