Give yourself plenty of time and room. It will happen.
You don't have to share all that you write. I have taken my journal to share some of what is in there, but not all. It's more a way to encourage me. Sometimes I write just one word or several words on a slip of paper and carry it in a pocket I can slip my hand into, to touch it and connect with it and find some extra courage.

It is different and takes some time to get used to the pace. It isn't easy to just sit and talk. It wasn't for me anyway. I saw my T for 9 months (a birth?! lol) before I could really talk. I just decided I was going to way whatever and take it from there; it might be important or relevant or not, I though. (Actually it's all important and relevant, I discovered). T has encouraged me to say "Anything and everything. Whatever comes to mind." so I have her open acceptance about it and that helps too. She did not hurry or push me, knowing it would come.

When I stopped pressuring myself and expecting to cover a lot of ground (instead of depth), then it got easier.