Just a thought, he might be inadvertently invalidating you when you do tell him things, making you feel like he doesn't care.

I have the same problem, as in going blank as soon as I get at T's. Or sometimes I'm experiencing a different ego state so what I was going to say doesn't feel at all relevant. I try journaling in between sessions, and even then it can be difficult for me to read to him something that I don't really feel at the time. Telling anyone something about yourself makes one feel vulnerable, and the fear of embarrassment or rejection may come up.

When he triggers you, can you think of what he said? Try to notice how you feel in response to what he/she says/does. Share this if you feel comfortable, if not, remember to write it down. It may help you figure out what is happening. I also am massively sensitive to possible rejection/embarrassment, so I totally get what you mean. With T often being seen as a parental figure, that would cause him to be able to affect you more than others. (Just one possibility)

Can you start with telling T that you have things that you want to say but you're too afraid of the embarrassment/rejection you might feel? This is where real healing can occur, from you disclosing personal information and having your T validating/accepting it. You are the patient and you are trying and doing things the right way. I do hope you can take a risk and see how it goes. Keep us posted! When is your next session?