Letters have been discussed here a lot. You can choose to test the waters, and note the reactions. OR you can change your behavior to SHOW HER how you feel. I believe this is better. Actions speak louder than words.
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712