Let's think about this another way. Is it possible that W is getting something out of the secrecy other than the two extremes of wanting to not hurt you and wanting an attachment with OW?
When I was with H, he had an ex-wife with whom he needed to communicate about the kids. She would use the communication as a route to constantly try to pick fights. She would over-communicate; almost daily messages about two teenagers was clearly not necessary. She was constantly manufacturing perceived crises with the kids in order to have a reason to communicate with him, and trying to call meetings with school personnel and therapists, trying to get him in a room where she'd proceed to talk about her feelings. When he didn't want to participate in those meetings, she'd reply, cc'ing the external people, shaming him and telling him that his unwillingness to parent with her was harming the kids.
Yeah, she was a real treat.
H would sigh, and show me the messages, and we'd decide what would merit a response (things that were actually about the kids and not her feelings/anxieties.)
I looked forward to the day that we could be free of her, when the youngest graduated from high school.
Now, looking back, I see that he didn't see it as I did. After 20 years with her, he had no idea what life without her spun-up-chaos was like. He wasn't reaching for it as I was. He was sitting on a fence, trying to bide his time and keep both of us happy with him. It looked like taking a stand, but it wasn't. Because as she piled on more and more harassment (shortly before we split, every message of hers had curse words and insults about him as a father), he lost the will to keep us his boundaries with her.
I've recently had the revelation that allowing her intrusions was something that was actually working for him. In my case, I think he liked that having this, er, Rabid Sister Wife type figure in his life because it allowed him to not have to fully commit to me.
I think he liked the power dynamic that she created within our relationship. He could choose to tell me or not tell me about her latest antics, sometimes shielding me from whatever it was because he "didn't want to argue", even though I'd worked really hard not to be reactive to her BS. He had this secret communication and this bond with another woman with whom he had significant history, and he could pick and choose whether to tell me about it. And he liked that.
Is it possible that your W is doing something similar? Does having this career loyalty to OW and excuse to communicate with her, and then a choice to tell or not tell you make her feel powerful? Does it allow her to feel in charge of you and your relationship? Does it make her view herself as the real adult and you as some sort of dependent? And, most of all, does it create a natural obstacle to her full commitment to you?
Maybe none of this applies, but the above was a revelation to me and I thought I'd share
