I agree with TL. Everything you describe I feel too and I would guess most all the parents here do now and then. The thing is to not be defined by it, and to have antidotes. Antidotes can be all kinds of things: a rich and full life, lots of interests, rewarding hobbies, friendships, satisfying work, prayer, exercise, goals, etc. You get the drift.
We all of us, have moments like you describe. Where are fear and agony and dread, and anger and annoyance get the best of us. Usually this is triggered by contact with our child. Either they try to seduce us into taking in and on their problems, or feel their emotions, or remind us of how bad we feel about their being in a bad state. So. They become our trigger.
I can't stand hearing his voice.
All of this is quite normal in my experience. I cannot stand for my son to call because he triggers me too. Because you see, we have become addicted to them. And many of us have inadequate defenses. What is it Kryptonite? Is that the substance, that robs your power, or is it something else? But this is not true. We can beef ourselves up. Or we can insulate ourselves, before we are strong. The boundaries you refer to are highly individual. There are no "right" boundaries in my experience. Just the ones you need to keep yourself safe.
He will be alone for the holidays which is a trigger in itself.
Life is a trigger. You have triggers. I have triggers. He has triggers. This will be his life story. Does he succumb each time, and wallow in the demon rum, or does he acquire support, community, practices, meaning, that help him to recovery. You or I have no vote in this and no control over it. I am in the same boat as you. It is horrible.
But it is our decision to make whether we begin to row out of the tempest to a beautiful, pacific lank, or whether we stay in the squall with them. I vote to row out of it. But it took me a whole lot of time and posting to decide that. And it got very ugly for me.
My son will be leaving his treatment program next week.
This is his business to handle. Not yours. But I relate very much to how you feel.
So far he is refusing to do sober living.
Again. His decision. You know that.
Maybe you want to ask what kind of boundaries you need? But first, I think you need to think about what you want. Identify what you are seeking from this situation. Everybody looks for something different. Why not brainstorm in a post what you would want. And go from there. When you write it down, you can read it, and your thinking/feeling process becomes clearer, and you can refine it. If you can identify what you want, the boundaries can come from that. We will be glad to make suggestions, when we know what the goal is you want.
Take care. Please don't be hard on yourself. This is hard.