Good step....as for the meltdown. It is tough, but it will continue to happen (both my kids have problems when they go to their mom's...even though it is every other weekend). I had a friend explain it to me as such....Each house runs differently and kids respond to that. It isn't necessarily that either house runs right or wrong, just that the difference can mess with the kids. Different rules, different schedules, etc mess with the kids balance. In the ideal world you and the X would get your households running the same in regards to the kids....but honestly your world is so far from ideal it is crazy.
what I have done (especially with my son) is I listen to how he feels when he is down there. I DO NOT make a single bad comment to him about it or address the X about it...I LISTEN to him. It makes him more secure. I also let both of them decide if they want to go or not...I don't make them go. That gives them some feeling of say in the matter. In the end this has made things better for everybody....The kids want to go see the X, don't feel forced into going, and everybody is more relaxed. Heck....If I remember correct your wife lives right down the street. It sounds like an open door policy would be awesome for the kids....Let them see which ever parent they want during the day.....as long as they sleep where they are supposed to. As close as you two live...it could be in the same house every night, but spend the day with whichever parent they want. All within reason of course.....but the kids are #1.