I am sorry that your son and you seem to be estranged right now. I wonder how much of it relates to his father.
Your letter is good and direct. However, I then tried reading it with the mindset of a 24 year old man who has a bit too much pride and an "I'm Owed" attitude. It possibly wont go over well with him. You may still be in a Detente.
I hope that I am wrong and it does cause a bell to go of in his head that he needs to respect and communicate with his mother as an adult.
