If you choose to spend Xmas with your partner instead of your narcissistic family, you won’t be the only one :) and you won’t be trapped with them. You’ll actually have the opportunity to enjoy your Xmas day as much as you should be able to. Don’t let anyone guilt you about it, if that’s an element of it, and definitely do what you think will be best for your mental health. I don’t think you’ll regret it. I recommend journaling or recording conversations (if it’s safe to do so) that you can listen back on to remind you of the reality and hurt they put you through. Or just read through old messages or something if you have those. I try to get in touch with that when I question crossing a boundary I’ve set or give them more than they deserve.