the role of a family is not to hold you back or make you feel guilty for wanting to spend Christmas with your boyfriend, it is to support you in everything you do. if yours can not handle that then it is their problem not yours. tradition is only tradition as long as you let it be.
i have not spent Christmas with my 'family' (i cringe using that word because mine are far from a loving family) since i was 19 when i realised my lot were detrimental to my well being! ok it did feel strange the first few years but it gets easier, even now since my partner died i still opt for Christmas alone rather than with that lot. I do not have any problems with it, it is me looking out for my well being and putting myself first rather than pushing myself to the back of the queue and bottling up the resentment.
At the end of the day only you can decide what you want to do for Christmas, but please do what you feel is right for YOU not what is right for anyone else.