I am sorry this is happening. You seem to be trapped in a viscous cycle. Here is the thing, you cannot change the course of things, but you can jump out of this trap at any time. This is taking up a lot of mental energy and causing you stress. It's not okay. What he is doing is not okay. Listen to your your instincts about her and if he's being honest. They are right.
Sometimes sitches like yours are a more complicated because they are not obvious or black and white. He didn't up and leave, he doens't seem to be having an active A with her, and he isn't threatening D. That doesn't mean he is being a good H and giving you what this M needs. When someone is all in, they listen and deeply care for their S and they will do whatever it takes to mend it. Including cut off all contact with a coworker, change jobs, and provide full transparency. I don't see him doing that. I don't see him doing much of anything.
I don't know if you read my sitch, or if I even shared much of this, but my H had a female coworker who was into him for many years. This started before we had any M troubles. She tried very hard to get his attention, gain his sympathy by telling him her problems, and would try and text him and befriend him outside of work. He didn't pay much attention to her. He also didn't draw firm boundaries with her and so we argued about that. When we started having M problems and split up for that 10 months, well she came on strong! In fact, he and OW argued about her too. lol. This lady started sending him sexy pics and tried to kiss him at work. He couldn't even tell his OW because she was jealous and insecure of their R (of course she was, she was just an A). So that was a huge lighbulb moment for him. What I had been saying (his W) for all those years was right about this coworker. Now he is deeply ashamed he didn't shut her down in those early years.
I don't know if your H is as aware as he says he is or is somewhat oblivious to how inappropriate his Rs are with women. He lacks boundaries and overall respect for you and the M. The thing is, I am not sure you can convince him. I tried for many years and my H did not get it! He thought he was just a nice guy, kinda felt sorry for this lady, and it did make his ego feel good.
No matter what your H is thinking/doing, I think your actions are the same. You are going to drive yourself crazy if you keep watching him, arguing, and going in theses circles. It's not working either.
I just wrote a long post to Meg and I think it applies to you to. Even if he is not having an A, you can still save yourself. You also send the message that you are done playing games. Let him be, start to detach, and don't worry about his response. You don't need this cr-p.
