I agree with the guys here. The S papers sound more like D to me, so if you sign them, I think you should go dark and live life as if she is no longer a part of it. Can you do that?

She will take her time enjoying being "free" with dating OM, etc. but you will be developing your own life. When the A fizzles she will either turn back to you or move on to another man.

I would not be in MC "with" her if she's S from you, but if IC is helping you, then you could continue that. She is not committed to your M or she wouldn't be pushing for this S. I think she is wanting to hang onto you just enough so that if her fantasy with OM doesn't work then she'll always have you waiting in the wings. That is what she needs to see....that you aren't second choice.

Is she still keeping the A a secret from her family and people at work?

It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!