My situation mirrors yours so closely that it is scary, right down to the timing of the bomb. Your W may seem calm about her decision but there are two answers to that. The first is that she has already had some time to come to terms with her decision. The second is that she doesn't want to show you how much she is hurting inside right now. My W is the same way; she always seems like she is at peace with her decision but I can tell that she isn't. I am sure that if you take some time and gain some perspective you will see that your W isn't at peace either.
My advice to you is spend some time focusing on what you need. Reconnect with friends, take up a new hobby, "find yourself" by figuring out who you want to be, and be the best father that you can be to your kids. And most importantly, take back your emotional life for yourself. I know that it is hard because I struggle with it on a daily basis, but the sooner you can let yourself decide what you are going to feel rather than just reacting emotionally to what she is doing the sooner you can be happy again and feel hopeful about yourself.
One other thing I would add is that your wife is right about you needing to move on. However, moving on doesn't mean giving up. Your R with your W is dead, I know you don't want to hear that right now, but there is nothing stopping you from trying to build a new stronger relationship with her if that is what you want to do.
M 39, W 34 M 15 S 14, S 12, S 9, D 7, D 6 Separated: 7/2/2012 Served: 7/10/2012 Divorced 11/5/2012