Nate, do not give her that letter, it will only push her further away... Just work on you and let her do what she's going to do. If you say anything about moving out, just say something like "that is what is best, I will not be a part of a 3 person marriage and I am willing to let you go"...
M - 9 1/2 years 5/5/16 - Bomb drop - 3 week EA 10/31/16 - We sold house 01/10/18 - D Finalized