I don't know; focusing on them, especially without getting any feedback from them (to know that they "heard" you) might not do much good? One can't get closure usually, alone, without the other person/situation providing it (when someone dies, knowing why/how they died, having a funeral, etc., for example). If writing like this works for you, then it probably will work whether you send the letter or not, since you are not expecting any reply? I wouldn't send it (though it is a great letter!) would not give this person any more of "myself", my thoughts, emotions, etc.