I'm presuming this is your oldest DD? Assuming she actually still wanted to spend that much time with him and was expecting the arrangements to be fulfilled, then pulling out now is cruel.
However, in the wider scheme of things, I actually think he is doing the right thing because it seems that unless he detaches from you Solost you won't be able to detach from him, even if your DCs are finding the situation confusing and bewildering. I think after the news the DCs have had about his other relationship, it would be really confusing at the moment to be all together at an event and overnight in a hotel - possibly giving them false hope again.
I really hope you use this as a catalyst to change the terms of your relationship with him and it's a shame he was given the chance to do this first.
I think when he said he had resolved to be more pragmatic in the new year, he meant that he was going to put his guilt to one side and commit fully to the OW. This is an example of it.
I know this is hard and I'm relieved you have admitted you still want to see him Solost but going right back to the start of your first thread, the only reason this selfish man would ever have come back to you was when he thought that he had lost you for good. It's a shame you still want to see him and would have him back, but you can't do much about those feelings and I understand them.
However, he isn't coming back and will want to less when he knows that he can still let himself in and out of the house and see you. You know that I think this is actually damaging your DCs now, when they need structure and arrangements to see him elsewhere and not in your presence, but all along, this has also been damaging you and your cause too. He would never have wanted you back while he still thought you would take him back.
It makes me angry that he has been allowed to flinch first and put more boundaries in your relationship, but he is at a glance demonstrating where his loyalty lies.
Please take this cue from him and start formalising contact arrangements and restoring your home to your fortress. A long time ago I advised you to act detached and you would become detached. It's not surprising that there have been huge stumbles along the way and I truly empathise, but for your own sake now and especially for the DCs, assume he is never going to change his mind and certainly not with the status quo as it is.
Make the New Year the time when you become like most separated families; the DCs see the non-resident parent independently and not in their home and you have no relationship with him other than a co-parenting one.
I predict that he will start being hard-headed about the finances, now that he has decided that he shouldn't wallow in guilt any more. Be even more hard-headed Solost because believe me, he will screw you over in a heartbeat now that he is losing empathy for your plight.
Part of me hates having to deliver these unpalatable messages Solost and I hope you understand that they are given with the best of intentions and certainly not to hurt you more, but I can only tell you how I see it now.