Christmas time/holiday time is one of those times where we are supposed to be of good cheer and put the past behind us and put on a smile. However, it's very difficult to do when being false isn't in your nature. I don't have solid answers, but I"ve not enjoyed Christmas time for a long time. But I'll echo what others have said, do something for yourself that day. Cook, eat out, dress up, dress down, watch your favourite guilty pleasure movie, doesn't matter what you do, so long as you do it for yourself.
Have you ever seen the original Terminator film? Do you recall when Sarah Connor was having a terrible day at her waitress job? She's in the back room smoking a cig, looking flustered, and her friend passes by and says: "Look at it this way, in a hundred years, who's gonna care?"
I take that to mean this:
No matter how bad things are today, it will pass, and things will change. Even if we are ready to jump off a cliff (and I've been there multiple times) that terrible feeling will go away and tomorrow holds an unknown promise. We are here for you on that day, and all days, just reach out and ask.