Do I think she is keeping both of us around to see how it all works out? Yes
Well of course she is. Why wouldn't she? She has an OM who meets God-only-knows-what needs of hers, and a faithful husband who rubs her feet, takes her on nice vacations, leaves her romantic little notes and is the world's best listener and an awesome dad, and this keeps her family intact.
I'm not trying to be glib, Sho -- I know you're hurting today. And you don't have to decide ANYTHING today, btw. But this is the problem with extending the "Plan A" phase past when you know about an affair, and they KNOW that you know. It only leads to cake-eating and limbo.
You need to remove yourself as Option B. It's "A" or "C", but not "B".