Last Christmas was just 3.5 weeks after I told my husband I wanted out. He only moved out this year in March so at Christmas we were still very much acting normally for our DS (who was 3 at the time).
It was awful. My little boy was so happy and all I could think about was how it was his "last family Christmas", how he'd never have another "proper" Christmas and the knowledge of what was going to happen seemed so terrible and unforgivable.
One year on and we're all OK, so much happier than I could've imagined a year ago. It's really difficult, especially at Christmas, to let go of the image in your head of what you thought your and your children's future would be, but if you're in an unhealthy relationship then that image is just an illusion anyway.
If you're in the same situation this year, either recently separated or in an unhappy relationship and contemplating it, please believe that it will be OK. That if Christmas has made you miserable this year, it won't always be like this. Hang in there 