I'm not sure what her intentions are/were, either, and I don't think W really knows... He did say whenever I was mentioned she'd say she felt guilty and awkward, which leads me to believe she's not interested in a poly relationship, she just happens to have feelings for a married man. I can see how easy it would be to develop feeling for someone who is helping you through what has to be a very difficult time (divorce). And I can see her enjoying the attention, especially after what has happened with her marriage. As W shares more (and he's sharing EVERYTHING with me now) I'm gaining more insight on everything.
No, W & I are not planning on any sort of poly relationship, either now, or in the future. This was just the best way he could think of to help me gain a understanding of this crazy situation we are in. And it has helped a great deal. I find that I am opening up a bit more to the idea that he could have feeling for someone else, though I am completely against any sort of physical relationship. I really cannot see that changing. But a few days ago I was completely against the two of them even remaining friends at all.
At this point, I have made the decision myself to reach out to M with W's knowledge, and see if it is possible to work out a friendship. This is with the understanding that the lines of communication must remain open, and that the relationship cannot go past friendship. W assures me he will do nothing to risk what we have together. A lot of introspection brought me to this decision, and since there is not a physical relationship involved, I began to feel that my demands on ending what has only been a friendship with some feelings involved, is perhaps unreasonable of me. We'll see how things work themselves out.
I'd like to add that W had no input on this decision. I've spent the last few days thinking, feeling, and seeing or hearing every word they have said to each other... He has not put any pressure on me what-so-ever to come to this decision. In fact, he's been pretty adamant about completely ending things with her. Since she is a co-worker for now, there has to be some sort of relationship left in tact. I'd rather he be able to be comfortable at work than to force him to cut ties with her and make it awkward for him to do his job.