It's hard to do. Very hard. But you have shown in your post above that you are aware of how you are supposed to act if her mindset is that she is going through with this and there is no stopping her. That's a lot of the battle right there. The friend role is VERY important.
I helped my WAW move out to her first place and on to a second one that was nicer. You can do it under the premise of you want your kids to see their dad helping their mom, doing it so they'll have a nice place to be when they are over with her, doing it just because it's what you would do for even a decent male friend, not to mention the mother of your children and your best female friend (I would assume anyway). Hold your head up high that you are doing this. The only caveat is: you need to say ONCE, and only once to her that it saddens you greatly that you two are in this situation, but that you'll give her the space she is telling you she needs.
I did end up divorced, but my XW and I are on great terms and if I didn't know better, I think she would come back for another try pretty quickly, though it very much would be a take it slow process. I attribute a lot of this to maintaing a cooperative and friendly attitude with her, and that included helping her when she needed it. I didn't have to, I was mad a lot of times seeing the demise of my marriage and I was hurt a lot of times too. But I decided the right thing to do was to act like a friend and someone she could still depend on. I think you have to maintain that attitude, hard as it sounds and may end up being.
That doesn't mean you overdo it, I think you should only help her with stuff you truly want to help her with or stuff that you wouldn't think twice about doing for a male buddy of yours. Moving is certianly one of those things though, and I can almost guarantee you will feel you did the right thing if you do help her. Might on occasion feel like you helped open the door to her leaving, but it really isn't that. If there is no stopping her from moving out, then I highly encourage you to do this as you state above and act like everything is ok..you can always post her to let off steam about how it's not.
I wish you the best.
M-34 XW-32 D-7 Found OM's presence 4/09 Separated 12/09 Divorced 8/10 GREAT relationship as coparents since 8/10