It is hard to fake the 'letting go ' so you have to get out there and let go. Make plans for future that dont include her. Yukky we know and it might not be the case. Right now you have to deal with the 'real' not the fantasy. She has gone.
What do you need to do to move on -- another job ? what ?
Once you are of the mindset that it is just about you and the kids, she will i promise feel it. It is simply a shift in the way you are. I dont believe you can act it, it just has to be.
Make a list of what YOU need to do for you, little baby steps if need be.