I'd lay low for a while to allow W to recover from the post-op and enjoy your time with the ILs. When W is somewhat clear headed from the operation drugs and things are a bit more settled, then I'd bring up the contact with the xAP and how it made you feel. NC needs to happen to protect the M and allow it to thrive in a stronger M. Frame it as respecting and valuing you. Then offer to aid her in the NC letter. There's a good amount of templates to look at if you Google 'NC letter to affair partner'.
You might want to have W read the book After the Affair by Janis Spring.
