Hi, Kat, those are very good points. However, xW's sister has been "friends" on FB for a long time now -- if xW wanted to keep tabs on me through her sister she certainly could -- and I have no reason to believe xW wouldn't have already.
The weird thing is that somehow xW has already been made my friend; I got a message that she accepted my offer to be friends -- How did that happen?!?!! I didn't send any such request! I think I need to contact tech support at FB and get this straightened out.
Now I could simply cut off the "friend" connection with xW, but that would definitely be seen as offensive. But perhaps that is what I need to do anyway. Like you said, my xW is not my friend.