I think trying to understand it may be your downfall, here, OP. You're not a secret drinker, you're not a secret smoker, you don't hide dangerous things where your toddler might easily find them. You don't have to understand. The whole point of splitting up (for any relationship, any time) is that the two people are too different.
He is continuing to treat you poorly despite your attempts to instigate changes. He is manipulating you into the guilty position by telling you how bad it will be if you leave, but how bad is it for you if you stay? You sound like he's driving you round the twist, and is willing to get behind the wheel drunk, endangering his own life, your life, and your child's life. How bad do you need to feel before it will be worse than how he will feel if you leave?
You are not responsible for him. His drinking is his responsibility. Even if you were unbearable as you suggested earlier, he still would have a variety of options. Imagine how different things would be if he chose, instead, to talk to you about the options/compromises you could reach by both making small changes. That's what a healthy person would do, in a healthy relationship. But he makes the decision to drink. It can't be your fault unless you are holding him down and pouring it into him, whilst he protests.
He is also responsible for the way he feels after you leave. If you tell him you need change, and if you don't get it, you will leave, then any feelings he has after you leave have been caused directly by him.
You need to get firm and stop doubting yourself. You don't like what he's doing so you need to stop putting up with it. It's not about changing him. It's about changing your view of the power dynamic, because at the moment, you give him all the power, and then take all the blame when things aren't to your liking. Can you see why it's all weighing so heavy on you? Take back some power. It's your life. You're in charge. You get to say what's ok for you and what isn't. You can spend time with whoever you like, or not. It seems you've lost sight of this.