I just read all 27 pages of this thread, and it's heartbreaking.
First off, there is no excuse or defense for her either lying to you or bringing another man into your intimate relationship. None.
But. I could be her. A husband who was happy just being in the same room with me. A husband who (often) gave so much of his heart and mind to his work that there was literally nothing left for me at the end of the day. A man who, while open to me in many respects, had enormously thick walls up against true physical intimacy (that sounds a bit different from your sitch in some respects, but it may have felt similar to her.) A man who always felt constrained and conflicted when it came to passion. A man who seemed more interested in "taking care of me" in the pleasure department, as opposed to "taking me" for his own pleasure. (Mind you, of course that can go too much the other way too, but either extreme is distasteful to many women.)
Let me tell you, that is beyond disheartening (and defeminizing) to live with long-term, especially if your primary love language is physical touch.
Was it his "fault" or did it make him a bad or insufficient person? Of course not. He was the way he was for a lot of very logical reasons (aside: what IS IT with engineers?) He was and is a great guy and the best friend anyone could want. But I wasn't getting what *I* needed to feel loved, valued, and cherished. (I am now.)
As far as the things she has been saying about wanting to stay in bed all day cuddling/making love ... I could have said exactly that (as unreasonable as it sounds). I call it "50-lb steak syndrome" -- if you've been starved for a long time, you build up an enormous appetite, at least in theory. What you are actually satisfied with eating when the scarcity is gone may be a very different thing.
I'm not defending her actions here. Divorce is a very big stick indeed, and not an appropriate negotiating tactic. Not to mention, if she has had her head turned with fantasy and attention from an OM (although it is unclear to me how much this is still ongoing), she is NOT doing her best thinking. And I think you do have to be willing to throw down ultimatums about her contact with him; it's important for your own self-respect IMHO, and also, she'll never value you or want you or take you seriously as anything more than a "Nice Guy" if you don't show by your actions that you value *yourself* too much to be willing to share her or play second fiddle.
Be that as it may .... compassion, comprehension, and empathy is always in order.
"Show me a completely smooth operation and I'll show you someone who's covering mistakes. Real boats rock." -- Frank Herbert