I'm sure that she thought it was strange that you wrote it to your son, at least I do, and may come across as you preparing to attack her to your son... Which would explain the only thing she said about it.
How would you feel about posting it here? Really difficult to know how much damage may have been done without knowing what it says... It is possible that she recognizes that she just saw your inner most thoughts and it could work in your favor, but again hard to tell without knowing what it said.
I will tell you that I wrote a letter to my W (I posted in my thread) owning up to my mistakes in our M, but I was strongly advised not to share it with her, so I didn't. But now that I'm piecing, my W and I were talking after my horrendous text messages the other day, and she made the comment that I had no idea how much I hurt her by my actions, so I pulled out the letter and gave it to her... It was the first time she's really cried thinking about us, and I think it did a lot of good at that point because it showed I knew how much she was hurting.
M - 9 1/2 years 5/5/16 - Bomb drop - 3 week EA 10/31/16 - We sold house 01/10/18 - D Finalized