Holidays are stressful in general. And so is divorce. Combining them can be the final straw that pushes some people into depression. If this is your holiday experience, get the support you need to make it through but don't be too alarmed. It's par for the course and next year's holiday season will be much easier.
It's upsetting to have an ex-spouse continue fighting with you after your marriage is done, particularly when the ex-spouse is your children's co-parent. Taking time to think about why this is happening and exploring the possibilities can yield helpful information and lead to new ideas about how to stop fighting and move yourself forward.
One of the tragedies of split custody is depending on the warmth between you and your ex, your child is out of your control. It might be for days at a time. You have to bury your worry and love, so that you don't waste the time you're apart -- so that when you do get your child back, you're not a clingy basket-case.