Jake, PLEASE do NOT send her a letter. You have admitted you are angry. These types of letters almost always do as much harm as they do good.
First off. You used the word "I", or "me" at least 70 times in that letter.
You are only painting yourself into a corner with a letter. You are angry and even admit you are all over the place. That is NOT a good time to write letters like this. Next week you could be sorry you wrote it. She could write back in anger and tell you yet again that it is all your fault. etc. etc....
You are pointing fingers at her and finger pointing and preaching.. That type of stuff goes in one ear and right out the other to a WAW. It does NOT work. This is just another attempt to "get" her to straighten up and try to control her by sounding tough. On one hand you say you "want to stay" married to her and it is bad for your child, and then a paragraph later you are telling her you don't need her and you don't want to be with someone who doesn't want you. You can't have it both ways and come across as STRONG.
What works the best for men in your situation is this:
LEAVE HER ALONE. Let HER contact you. When she does, be nice, but be vague. End all contact FIRST when she contacts you. You don't end contact sounding angry, by being rude or by coming across as pouting. That won't get you where you want to go. "I need to get going because I was just_________(fill in the blank)(walking out the door, or on the other line, or right in the middle of something." etc etc... not rude not mean, but short, firm, mater of fact. NOTHING ELSE. Over and over and over. Not for one day, but for MANY days. Consisten lack of pursuit. NONE. She contacts YOU. Wait her out.
Come across as matter of fact, in a hurry to go somewhere, busy. Busy men are attractive. Men don't have time to chit chat on the phone. Men are DOERS. Men don't have time to write letter like this. They just leave the woman alone and do action items.. Go to ball games, hunt, play sports, have hobbies, jog, work out, go out and have fun.
LET her go by action and silence. In other words.. THERE IS NOTHING MORE TO TALK ABOUT. "I get the message honey, you don't have to hit me over the head with a two x four for me to get what you mean".... "I got it"
You need to let her believe that you are already under the impression that she HAS ALREADY made her choice and you GET it.
If she truly loves you she WILL come back without you doing another thing. You are only keeping this dragging on. MOVE on without her and without telling her for now. You CAN tell her all this stuff later AFTER she comes to you and ASKS. If not.. So be it.