Don't wait until you are washed over with anxiety/emotion to decide what to do. Think right now about the best course of action to keep your boundary/wall strong. I'm thinking it would be to not talk to him today since you already know he's drinking. You will see what happens tomorrow morning.
You can, right now, send a text message saying "I just got home and see you called. I'll talk to you tomorrow. Bye." and then turn the phone off so as not to temp yourself and listen to his messages.
Your boundary is strong, your personal integrity of not worrying someone is upheld, your evening is drama free. win win. No need for explanations. Those are just part of the unhealthy dance you guys are doing.