I don't as much experience with this from a difficult child standpoint, but I do from a divorce standpoint.
It is hard..
The first year my DEX was gone, Halloween was the first "holiday". difficult child was 14 (but this kid never outgrew Halloween!!) and she decided to go trick or treating with the little boy she babysat for. I was totally cool with this - it gave her the proper excuse to still go out, but it was so hard to be here with the doorbell ringing and the cute little kids,in my empty house so suddenly alone.
The first Christmas without DEX, we changed our Christmas Eve routine completely - went with my sister's family to their church, niece's house for dinner, home to watch a movie. It helped to change things but to still celebrate the holiday.
As her GFGness emerged,she would sometimes use the holidays - as to which parent she chose to be with - in ways that were less than easy on any of us. Again, we changed and adapted. I am fortunte to have a very cooperative DEX as far as this goes.
The holidays are hard on anyone who is struggling with a life change. Be kind to yourself and know that it will get easier.... not easy, but easier.
Dash