Knowing that your W is involved with OM, you need to remove yourself as the back-up plan or as a place set that meets her need for "family."
Just focus on business and the kids. Being nice doesn't mean you slobber over W like a puppy. One can be polite and cordial without being rude or jerk.
I would cut down on interactions with W that are being used to temp check or find ways to get close in physical proximity. That needs to stop so W can sense and see that you are not going to be her sloppy seconds.
