Enjoy the Christmas party. Why not just play it by ear. Try to enjoy it and stay as long as you do. I understand being sober when everyone else is drunkily laughing at drunken jokes can be heavy to support.But maybe just maybe it could be fun.
I would put having fun ahead of letting H get a glimpse of how stunning you look in that dress. I'm sure your D will tell him how well you looked!!
Plus staying out later could make H think more. You could be having so much fun. You are dolled up. If the party isn't fun, go do something else afterwards on the way home.
Best wishes
R 25 years M 14 years S11 & S13 Working on it alone since Oct 2014 M in trouble a lot earlier (~2 years) Feb 2016. 1st R chat in a yr. Next R chat Aug'17 Still together