Definitely give them the letter and like Canyon said explain in the letter your concerns about opening up etc. I struggle a lot with talking but I've been seeing my T for over a year now and he has been patient, he knew from the start how hard I find it, and still do. He is also a NHS T and hasn't stopped it just because of not being worth taxpayers' money. Everyone deserves help and support, and I think it comes with the job to expect everyone to open up at different speeds.