Hello,
I think that for him to go away with his adult daughter for her 21st is a magical and amazing thing that they will be able to treasure for ever. I also think he did stick to the boundaries that you set, regarding four nights and I don't think I would count the flight back as a night away.
When and if you go to NY together in the future it will have a completely different dynamic as you are a couple so try not to live from your initial reaction - which is understandably I would love to do that.
Please try and find ways to reframe your thinking on this trip and take a bigger view of it.
At the moment you are thinking of all the negative things and how hard it is going to be for you. The more you think like this the more likely it is for that to happen and you will fall into a vat of misery and self pity!! This could go very sour very quickly - But its not too late!!
Be as proactive as you can be:
Make a list of the things that you can really influence while he is away to make it as stress free as possible.
-Places you could go eg book them all into the leisure centre childcare for two hours so you can go to an exercise class/swim/shower and have a coffee.
- Ways to make it easier on yourself - don't do bath time every day, or only bath certain children on certain days!
- Lists of things your love eg Order in the takeaway that you love but he doesn't like and scoff the lot.
Try to be as open and as encouraging as you can eg: Be pleased for them, be interested, give the trip your blessing - it will make for a much more harmonious family life.
In reality you probably won't miss him and you will get to watch what ever you want on the telly.
When my husband went away for an amazing stag do I thought it was going to be terrible but I didn't even miss him!