If I have to sign, I probably will do this.

I actually already started a draft. (It was my first reaction after I received the evaluation). But while I was writing it, I feel I am doing a lot of explainations again. I hated this "have to explain again" feeling for the last 6 months.
The fact is, if I write this, it will become very obvious to his boss why I am leaving. I have not decided if I want that.
Thanks for your suggestions.