As a few of the others have said, it's likely that PPD is playing a part in this - some of the most ridiculous things are magnified into "too big to stick it through" for a woman with PPD. It's amazing how profound it can be. But I also agree that it sounds as if she's been planning this for a while. I disagree that there may be a third party involved, not every woman leaves a good man for another wo/man, plenty of women just want their own space. We'll never know her particular feelings on this, and I don't think the speculation is helping Dan any.
Dan, you're hurting right now. I believe it's ok to be hurting and to let yourself feel the hurt, but you will also need to be able to set it aside at times to protect your kids and yourself. I hope you made it home safely last night, make sure you are very careful with the beer for a while. CD has given you good advice as well...
Finally, we're all thinking of you. You'll pull through this, one way or another and come out all the stronger for it.