Anxiety even though I want this? Trouble communicating

First things first: I have BPD (quiet BPD), and "fear of getting close to people" is one of the main symptoms, which probably doesn't help...

I've recently started a D/s dynamic with someone I really trust. We've been talking since July and he's just been extremely patient with me (anxiety made me shut down a lot at the beginning and I just wouldn't talk, at all. lol.). We've had our first session two weeks ago and it was good. We're seeing each other again tomorrow.

We're slowly introducing some rules (nothing crazy, literally "keep a journal" and "text me good morning") and there are times I start to feel claustrophobic? I'm so scared of commiting and being vulnerable and messing things up. It's a rule so obviously he won't and yet my brain goes "what if he gets annoyed by you texting him 'good morning'"? 😭

The other issue is that I'm so bad at talking about things that make me anxious. This is not his fault, he never ever gets angry with me whenever I bring up something like "I've been panicking for the last two days cause you didn't answer that message..." or something dumb like that. He apologizes and thanks me for telling him. He knows I overthink a lot.

After our last session he tried to prompt me to talk about it and I just went "oh I liked everything :)" then just proceeded to evade all subsequent questions... A week after that he brought up the topic again on a call and told me to write it down if I had to but to tell him what I liked/didn't like and just give him some more details. Which is fair. So I texted him afterwards and even brought up something I'd like to take a bit easier in the future. I was pretty proud of that.

There's also an element of shyness/embarrassment beside the anxiety.

I hate it, though. I hate shutting down in the moment and I hate being so scared of bringing things up. I know I have to. I've been improving, sort of, but it's too little and too slowly. I've been thinking about just asking him to not let me get away with "everything"/"nothing" answers for tomorrow. Basically waiting until I manage to actually talk about things.

I don't know. I feel like such an idiot bringing things up over and over again. He knows I'm a nervous wreck, what's the point in going "hey, I'm a nervous wreck btw" yet again.