Oh I wish I could help you. I was in such a fit this week that I never even read your post until today. SORRY!!!!
I hope you find lots and lots of help here and don't ever worry about the responses. Sometimes there is time and others not. Everyone knows!
As far as what to tell the kids... I always say "I don't know" If you tell them something is not going to happen and then it does, it breaks their trust. You can just tell them you don't know because you don't or tell them you don't know when you aren't ready to share the truth. That's what I do anyway. I know at times the limbo is also hard for kids, but let them know there will always be love and joyful things coming for them no matter what happens.
As far as your dh goes, I have never been in your exact spot. I have been in many relationship struggles, though, and these past 2 years have taught me a lot. The best thing I've learned so far is that you have to really figure out what your demands are and stick by them. You have to take your power over yourself back. Your dh can't have the power to decide your future.
I would go on the trip (possibly even not send dd to ballet that week and make her first day the following week. She won't miss anything on the first day and you can have a re-do when you return)
Like I said, not in your spot, but know that I'm just a fork in the road aways from it. I've been blessed with a happy marraige, but I'm not naive. I have a plan if it happens that is swift and detailed (happy to share if you are interested) so please know that we are all in this with you!!!!