That's unfortunate that you feel trapped and unable to relax. I don't know your exact situation.
But this is something that I have to navigate as well especially with certain family members. It might be helpful to explain that you have two different modes. And to explain that when you act like a kid you are just as aware of how people treat you as when you act more mature.
Also, it might take some of the stress off if you don't view acting maturely every so often as donning a fabricated identify. I mentioned earlier that it might just another mode. Though it is one that you can't maintain indefinitely.
When I was in undergraduate, I would try to stim or act immature when I was alone. For example, I would stim when I was walking alone between classes or when my roommate was gone.
I still do the same thing. Largely, I switch or stim around people that I feel safe around. I'm aware of the switch, and I can stop it if I wish. But it can't be stopped forever.
Does that help?