Hi Maria, Saffie is right! don't send the letter,well not in temper-wait. Me I'd be tempted to gift wrap him,tie a ribbon on him and deliver him personally, but then I do have a hot temper, very slow to anger but oh boy if you do it's like "light blue touch paper and stand well back".
I think it is frustration more than anger with you,and who could blame you but you have gotten this far,he has started MC but at the end of it all IS how much time have you got? Is the love you have for him enough,will HE be enough for you even when he is well again.
You have grown and discovered who you are and what you need because of the situation you found yourself in, he has got to get back to the man he was and then start catching up. No quick fix,light bulb moments are rare but can and do happen. I guess the dreaded P word is still not allowed so maybe perserverance oophs thats P as well.