Taking care of something for your son IS the right thing. And you can agree to disagree with Gym Woman but your R with your son and how you handle your arrangements regarding him are NOT her business at all. If Josh ever told me how to handle my kids - I would tell him to BUTT OUT.
I can understand GW's frustration with your ex wife - heck - I am frustrated with your ex wife but then - that is NOT your R with her. If I were you - I would minimize discussion about what is going on with your ex. And try to stay out of the drama! Josh was frustrated at my upsets with my ex in the early days but I realized it was taking a bit of a toll on our R. He also told me that the fact he continued to push my buttons was a sign that I was not truly "over" him. And in hindsight - I think he was right.
When I finally stopped letting Chuck have such an effect on me. When I didn't respond to the snap of his fingers or go off the deep end for the horror he continued to bestow on me - everything got better.
Put it this way. You KNOW what your ex is like. Just always expect her to be that way but don't bait her or fight with her. Just do what needs to be done then walk away. Funny how they stop fighting with us when they don't get the attention they crave. Liken it to a demanding, spoiled child. Hmmm - see the connection.
I'd talk to GW about this and her perception of "lying by ommisson" - how about "sparing her the gory details". I think that you need to tell her you'd rather deal with some of the yucky stuff from your past R without involving her in all of it. & she should be mature enough to handle that. JMHO.
And you DID do right by just signing the paper. You knew it was the right thing to do. Listen to your gut. Barb