Hello Enlightenedcynic, I am sorry to read of your troubles. I could be using the old saying"There but for the grace of God go I" because my wife is active, I am "inactive" and she knows me to be confirmed in "apostate" thinking lthough I still attend some meetings with her and am well known among the congregation - albeit not doing anything but attend. If Sister BluesBrother ever came to the same conclusion, she could shop me at any time. But she knows better and wisely keeps silent.
As for you, I think that you have the moral high ground here. If your wife approaches the elders, it will be her that is seeking a separation, in direct violation of Bible law for wives and Watchtower counsel and policy.
You are an active witness, on paper at least and that is what counts. You have not endangered her spirituality, far from it - you study with the family. She is the one seeking to break the sacred marriage vow.
As for the pieces of paper? they can be explained - research , questions, you were thinking of asking the elders about the U N thing....
As for sex? I would say nothing. Nothing at all. You have no need to. The elders would then just have her confession that she indulged in whatever practice was described. Reminds me of a hypothetical posed at an elders school once . "If one person confesses to something and the other does not, treat the silent one with the benefit of doubt since not 2 witnesses, but treat the confessor as a self confessed practicer of wrongdoing" With logic like that, no wonder the organization is in difficulty! but it may work in your favour.
So I sincerely hope that you can pull this through and save the marriage . If you play it right the elders will have to be on your side.