"She made some poor decisions regarding spending time with the kids last weekend."
out of your control... How she decides to act is her decision... If it results in safety issues for your kids then either you or the law will step in....

She began crying and worrying that I am going to try to get full custody, and so on.

Let her worry.. If her behavior is that bad around the kids, then she should worry.... 50/50 split is most likely though.

Obviously she is still planning on the move out.

find her a place... suddenly she won't be so sure that moving out is the right move.

What do I do when she is putting her personal satifaction in front of the kids' needs time and time again?

Again, hard to watch, but it is really out of your control. Perhaps you can write down days and when she puts herself in front of the kids.... If custody comes up as an issue, then you have some documentation or witnesses.

This is very uncharacteristic of her. She has changed in the head.

I will ask you again... Is their another man? When people's needs aren't being met, Others can/ will step into meet them...People in affairs don't act normally.... Did you ever hear of the lady that drove all the way across the U.S. to confront her affair partner? Scott Peterson killed his wife and their unborn child when he was in an affair.... People who are "IN LOVE" act very differently than they normally would... and yes it is important to know if their is someone else involved in your sitch...