I wouldn't. I've done so in the past and all it has gotten me is more hurt.
Is worrying about how it affects him just another part of codependancy?
Probably, yes. What you SHOULD be focused on is YOU. And how to get yourself feeling better, without HIM playing a part in your doing so. Because he can't really get you feeling better any more than alcohol can get HIM feeling better. We're all broken. And it's too much, really, to ask an alcoholic or addict, someone who is weaker even than we are with their monkey on their back, to help us.
Is it healthy to feel like I'm sending the anger in the right direction?
Do you mean towards him? Do you mean in the letter? Do you tell him how much HE hurt you and how much you sacrificed? And do you point your finger at him or his actions or his alcoholism? In other words, blame him? And ask for what you think will make you feel better? Because if your question is meant to ask whether or not directing your anger at him is healthy, my answer would have to be no. Not healthy. When my expectations don't get met, I get real angry. Spitting mad. Seriously. I would hate to be on the receiving end of my own anger. How about you?
I just don't know what to think or feel any more.
Al-Anon can help you here. It will give you new perspective. And new words to describe what you are going thru and have gone thru.