Yes this has already come up in March! Dp wants to have a New Years party at our house, we also have 4 teenagers between us and he’s thinking it would be nice for them to invite a friend too. They would love that, I’m the only kill joy really, we’re getting married this year too and at the moment I’m up to my eyes with that. The thing is none of my close friends or family live anywhere near me, as I’ve moved around both my parents have recently died so I probably wouldn’t invite anyone so would just be his friends and family. Plus all the work that goes into it, plus my health isn’t great I have fibromyalgia and constantly have headaches. No one really understands, I know I’m being selfish aren’t I , should I just do it for everyone once, I just can’t think about it with organising wedding too.
There is no way on earth I would host a New Year's Eve party, so YANBU at all! If, as I suspect will happen, DP gets his way and the party goes ahead, tell him that you will not be doing any of the shopping, cooking, cleaning etc in relation to said party, and it will all be up to him. And do not back down.
When it comes up again (surely no sooner than early December) tell him that you will be delighted for him to throw a party and will treat yourself to a new frock and a hair appointment. Then let him get on with the organization and the work involved