I have tried not to say this, and I hope it doesn't upset you too much - but then you probably won't agree with me anyway, so I should probably stop worrying about it anyway! Anyway, to get to my point, my viewpoint of this situation is that it is your Dad's fault that your Christmas Days have been ruined, not his first wife's. What on earth is, and was, an adult father doing in indulging/letting himself be noticeably upset on Christmas Day, every year, for 40 of years?!? He is completely pathetic, and weak, and indulgent, and performative to behave like that, and ruin all of his 3rd daughter's Christmases in such a selfish manner.
In fact, his behaviour is so performative that it leaves me doubting that he actually cares very much about any of his daughters. His selfishness as an adult in ruining his second family's Christmases is actually practically unbelievable, or at least it should be!
There is another thread trending at the moment, which mentions Emma Thompson in it's headline. Please read, even the first two pages, of that thread @iamsoashamedofmyself All those mothers who are putting on brave - and far too often - incredibly brave faces, so that their families, particularly, of course, their dear children, can have a wonderful and magical Christmas, just shows that the thing you should be most ashamed of, is your father's behaviour over all these years, but especially when you were only a child yourself.
However, you appear to have been a fully fledged adult for a long time now OP - unless of course your Mum and dad had you very late, which I will assume for now is not the case - so please don't let your father influence you to such an extent, that his annual 'performance' becomes something that you either share, or take over the responsibility of, by appearing to join him in making sure that Christmas Day is always miserable for those around you.
I think that one of the best things you, and your dear - probably long suffering -Mum, if she is - hopefully -still around, can do, is to celebrate Christmas without your Dad at all. If it is too late to do that this year, then tell him later on today what his behaviour looks like to people outside of his immediate 2nd family, and see what his reaction to that is. I don't know what rose to say to try to convince you to at least consider what I have said here, so I will just finish by hoping that you can have at least, a Happy Christmas.