Duke, I know it's hard, but you are absolutely doing the best thing. Protect your time with the children - they need you. Since your WW has proven to be difficult, you really need to protect yourself. You've been gracious and kind, and you can continue to be. Just don't let yourself be taken advantage of any longer.
Don't worry about what she says she is going to tell the kids. Take them shopping when you have them next. Quality fun time with Dad!
Quality fun time with Dad!