Tea,
I here your distress over these past events. I think it would be good to get them out of your head, internalising these things is so bad for us...the voices surrounding the secrets get louder and louder until we can't bear them anymore and maybe your t can help normalise them. What you might think is bad, others don't.
I think taking a two hour session will be a great idea and shows fantastic self care, congrats
I also hear some hesitation to broach the subject. If you are not ready to revela your secrets then maybe now is not the time. You have kept them for so long, why rush now? Only you know when you are ready, not t. Maybe writing the letter will help you process how you feel about the events now and help clarify if you are really ready to let them free? if you write the letter you don't even have to give it to t. I have wrote her hundreds of letters and never sent them because just the act of writing them and processing them helps.