I have been there in a similar situation. I would think she has been planning this for some time and gathered strength while you were gone. You did not do anything wrong, despite her claims. I would suggest:
-Get back in the house. You may stand to lose ground with custody. Sleep on the couch if you have to. In my state my wife could not ask me to leave. If she asks you to watch the kids while she goes out, hire a PI. Collect as much evidence as possible WHILE remaining absolutely silent, no matter how much it hurts.
-hire an attorney. Do not get caught off guard if this moves swiftly. File for temporary orders ASAP. this protects assets, spending, custody arrangements etc....if you do not move back in.
-collect all financial information and make copies. Freeze any joint credit cards you can. An MLC person with carte blanche access can destroy you financially.
-find whatever coping mechanisms you can...gym, church, friends.
-do everything you can for the kids. They will need you badly.
