See, the thing is that pushing yourself through it, AND staying home out of self-preservation are both valid options. BUT, only one of them is appropriate and none of US know the answer to that.

The question is your attitude, gutt-feeling, where your "heart" is at... however you want to say it.

Deep down, what is it?
Either "I don't waaannnnaaa!!" in a foot stomping Lucille Ball style? Then you need to rethink yourself. As others have said, family is work, relationships require work. And that work is often putting ourselves out a little bit. And you've had some great suggestions to prepare responses on how to deal with questions you don't want to deal with!

But you may take a deep breath and looking inside yourself find that you truly don't have the reserves of emotional energy to go through it. It's too hard and too personal and you're in a place where you're honestly feeling weak. That is OK. Setting a healthy boundary for a time to protect what you need is not only valid, it can be crucial for you to succeed and you need to find a way to tell your BF what your needs are. To do that right you're going to have to be vulnerable about it. It's not going to be easy either way.

I so feel you. We've been so some intense family trauma and have had seasons where we withdrew for self-preservation and seasons where we had to suck it up and participate because we knew that our motivations weren't valid and relationships needed to come first, or even be mended.

I hope that whatever happens ends up a good experience of acknowledging your needs and standing up for them (or to them ;-) )

First off thank you everyone for all the great responses, and all of you had something helpful to say and I really appreciated it

I sucked it up and went. I think I was psyching myself out a little to be honest. It was fine. No one even noticed that I had lost weight, or at least they didn't bring it up. I ate the amount I normally would, just with more salad and less potatoes, and I was brought the second biggest piece of dessert (Some lemon cake/tart thing that is my favorite!) Ate it all, probably shouldn't have but I had dragged myself to the gym for two hours yestereday, so I think I about broke even on the calories front I was glad to see our foster nephew, hes the cutest thing and so entertaining. That alone made it worthwhile

Thanks again everyone!