Oh yeah, this is VERY familiar to me!

Some things that have worked are writing things down - either in an e-mail (if your T does e-mail) or in a letter that I bring to session.

I've also told him "there are things I need to tell you and I don't know how". That usually leads to a discussion that is really helpful for building trust and connection, and eventually leads to me being able to talk about whatever the thing is that I need to talk about.

For me, EVERYTHING feels really hard to talk about in therapy. Sometimes I just have to take a deep breath and do it.