Do nothing, just detach and GAL. "I feel these things MUST be communicated somehow.." Of course that's how YOU feel but a trip to the zoo is NOT a whole-hearted commitment to work on your M.
If you feel you need counselling for YOU...by all means do it. It is her choice if she wants to ask YOU if you want to do MC, or if she needs IC. And the sex/STD stuff? Not really relevant until or unless you guys start sleeping together again as part of a piecing process...but it seems far from where you are right now, so I wouldn't give it any thought at all.
I've found reminding myself of the pursuit/distance thing really helpful. GAL your head off. Focus on you. Her work stress? Meh, not your business and why would you feel guilty? Did you put a gun to her head and force her to have affairs? Some of the guys who post here have some useful man stuff to say about respect and no more mr nice guy. As a woman, I think respecting my man is really important without wanting him to be a nasty chest-beater!
Me: 53 H:38 T:20 M:14 BD ILYB etc 10/15, H diagnosed severe depression S 1/16 PA 4/16 H filed 1/17