It's like you've been listening in on some of my most recent sessions.
I'm going to steal a page from my T's playbook and ask you: what do you think will happen? Play it out. What bad things will happen if you give up too much? It doesn't have to make sense.
And then, what in your past makes you think that will happen? Where are those ideas coming from?
For me, at least part of the answer is, I'm always afraid to tell someone too much about myself because I'm afraid that if they really knew me, they wouldn't like me. I imagine this particular thing has a lot to do with the disparity between how other adults, like relatives and teachers and friends' parents, seemed to see me as a kid, and how my mom seemed to see me. I was very popular with adults because I was polite, attentive, did my schoolwork, and didn't cause trouble. But to my mom, it felt like I was barely tolerable. The implication was always that my teachers wouldn't like me so much if they had had the horrible misfortune of being my parent (I don't remember my mom actually saying this, but I wouldn't be surprised if she did).
So I definitely get the push-and-pull... on one hand, I SO want for someone to really know me AND to really like me. But I'm so afraid that they won't that the risk seems unbearable.
Baby steps, southpole. This is a baby step in the right direction... when you survive incidents like this one (and possibly even benefit from them

), you'll start to grow more confident in your relationship with your T.