Christmas - Dealing with family expectations

Hi everyone!

It's the time of year when my family start asking me what my plans for Christmas are. I'm an adult who was diagnosed a few years ago. My family tend to get together with lots of people in one house on Christmas day. I always find this difficult to deal with. The last time I attended this celebration, I couldn't eat and I spend the day crying and hiding sat on the floor in a corner of the kitchen. 

So what's the problem?

Only a few very close members of my family know that I have autism. On the day I received my diagnosis, I was told by my mother not to tell members of my family. Since then, the reaction of those who do know seems to be to pretend I am not autistic and I feel a lot of pressure to 'act normal'. I think people feel very awkward about it and don't know how to respond but it makes me feel like its considered something shameful. I don't want to be ashamed of who I am. I can't stand people touching me and I've caused problems at family gatherings before by having a strong negative reaction to hugs, kisses and the like. I hate not being able to explain why I behave the way I do and I feel very isolated from my family.

So back to Christmas.

I don't want to make plans for Christmas, I just want to spend the day at home with my partner (who is the most amazingly supportive person in the world) but I don't know how to tell my family that I can't handle our big family get-together. I would also like to get more involved in family gatherings around the festive season but there's so much pressure to hide my autism.

Can anyone offer any advice on how to deal with the stress of Christmas or how to deal with a family who don't know about autism?

Thanks for reading my long post, I'd love to hear your experiences.