Luckily I'm not around people enough that I have to fake it on a daily basis. I only put on a mask when I'm at my appointments for therapy and see my psychiatrist. But to be fair, I'm also the type of person to smile and laugh, then suddenly burst into tears... But the thing is, with friends it's different. My friends are very aware of my struggles and when I don't smile or laugh, it doesn't mean I'm not happy for them and they know that. If these are people you can be vocal with and just be like,
hey, I'm having a bad day, but I just want to let you know how happy I am for you / proud of you. That seems to do the trick. Because you are validating them while also expressing how you're feeling... But communicating with people in general can be such a complex task. All of us are usually tired and just want to go home after it's all said and done.
Like you I've also dealt with childhood abuse and it impacts how I communicate with others, right down to how I behave physically... I was out in the city with my friend one day. and I always kept walking behind her or just hiding away. She kept asking me why I was doing that, if I was okay, etc. But then she realized it was due to the trauma I've experienced. I never knew that it was even like that until she pointed it out. Another thing I tend to do is apologize for no reason, always. We were hanging out in her apartment and all she did was look in my direction, and I was so quick to say, "I'm sorry." To which she replied, "Why are you even saying sorry? I just took one glance at you and you're apologizing, why is that?"
I hate how our childhood fucks with our wiring. And I am so sorry you had to deal with that as well.
Sending you lots of love and support.