I would be carefully with sending a letter, particularly an angry one.

See, one time I wrote T a letter and when I saw him in session I told him how I had wanted to send the letter. He told me that it was better that I didn't because of how things can be easily misunderstood through writing-- because there is no emotion or tone of voice to attach to it. Instead, I shared parts of the letter with him in person.

I think you have every right to be angry-- but if you intend to con't working w/ your T, I think you should share those feelings with him in person.