W will do exactly what she wants. The question is how far she has to push you away to get the space she wants. Pretty far it seems. She is friendly to you and you are all over her and her sh*t. That will teach her not to be friendly to you very quickly.
Sign the agreement. A few months from now she will be much less generous and you will be kicking yourself.
You absolutely cannot control whether W dates OM, has sex with OM, has OM at Xmas, makes pancakes for breakfast with OM with the kids. Drop it, now. She knows you want none of it, you can't control it.
If you want to do something, do it legally. Get it written into the agreement and make it a business matter. OTHERWISE BACK OFF.
Quit lying to yourself. GD is right. All that stuff is all about you and the "nailing" comment is passive-aggressive as hell. Passive-aggressive is about as unattractive as a person can get without throwing stuff or hitting. Something to try to recognize and work on...
Somewhere there is my water cooler post. Read it. Quit glomming onto W. Give her 100 times more space than you think she wants because right now you are just not getting it.
As for validation -- yes, it does sound like it was coming from a bit of a better place. But you are still keeping W from getting any of the space she wants.