I Am Very Selective When It Comes to Letting People Get Close

I am usually content with listening to people tell their stories and im usually pretty good at making people comfortable because I typically don't judge their choices because I know how horrible that would feel. however, im too scared to let people in and I tell them the superficial childhood fun stories because letting my emotions out scares me because it makes me vulnerable and I would rather avoid that feeling that confront it. as a result, it tends to keep me a good distance away from people unknowingly while they feel very close to me. and I should want to tell them things but there is really only one person who knows everything (and even then its not EVERYTHING) and that is because we grew up together. I feel like there are pieces I share with each person but no one knows the full picture. I wish I was more open and unafraid.