sports and poly
There are all sorts of potential reasons why your wife shut down recently. It might be she is overwhelmed with feelings and can't process any more, even if you need her to. She may not want to hurt you by openly discussing what's going on with her, your relationship, the relationship with the friend. (Gecko has a recent thread that touches on this.) She might be so anxious and fearful (losing you, losing the friend, losing the life she knew) that she shuts down.
I know I shut down when I can't process something anymore - because of pain, or exhaustion, or just too much-ness. I wish I had something more immediately helpful to suggest than being as patient as you can manage. And, yes, she needs patience with you too.
Also I was struck by the analogy of being the benched player waiting on the bench to be called in. You were the star player, lets say in basketball, and you're good, so there was no competition. Now, you are still a star but not the only one. To extend the analogy, your wife is asking you to be a team player more than you ever have been before. This is very, very hard.
Also, there is the point at which the analogy breaks down. If you and your wife are working towards ethical non-monogamy, you are NOT actually in competition with the friend for your wife. I have no doubt that it feels that way. But you are not replaceable; you can't be swapped out with a new model. You contribute something unique and irreplaceable to your relationship with your wife. Perhaps once your wife can process and talk things out with you, that will become clearer.