I relate a lot to this, it takes me a very long time to feel comfortable enough to be truly open and honest about everything. I try never to lie directly (I have though) but I often lie by omission. But I will say this, the more I open up and stop avoiding topics, the better I feel. It's uncomfortable to talk about it and I hate it while I'm doing it, but I know that I can't ever begin to feel better if I am avoiding some of my issues.

It helps me to tell my T "there's something I want to say, I'm just not sure how to say it." I had been witholding my eating disorder from her for MONTHS, the whole time I had been seeing her... I was leaving out this very large part of my mental health. I got to the point where I was embarrassed and I felt like it was too late to tell her. But I was very very ill and I needed to ask for help. So I told her I needed to tell her something but I wasn't sure how. She gave me a minute to think about it, and I just took a deep breath and jumped right in. It was very scary and uncomfortable but I am really really glad I told her. I'm in a better place because of it.

I know that others find it easier to tell their T something in writing rather than out loud. That's not something that helps me personally, but if you think it would work for you definitely give it a try! And I also do what DP does, between sessions I write down things I want to talk to my T about. Sometimes they're small things, and sometimes they're "big" things that I need to tell her but I need some time to work up the courage.