As I was reading your letter what I was actually thinking is this is a letter for him to keep for himself when he leaves.
I don't know your wife but I am familiar with alcoholism and what that does to a family. Your wife (I assume) is not blind nor stupid. Everything you have said she has probably already thought, in fact:
Her drinking slowly increased, until a point in May this year when we had another serious chat. For the first time ever she admitted she had a problem and that she hated who she became when she drinks. She promised never to drink again. That lasted seven days.
So yes, she does know, she does think about it and she is not willing, at this time, to do anything about it. This is out of your control. The only person you can control is yourself. If you do not like her drinking and you do not want to live with an alcoholic, you will have to leave, that is really the bottom line.
I truly don't say any of this to be harsh but there is a reality here that you might be overlooking?