You know something? I am not going to tell you that your husband is a monster, because he isn't. Every time he has promised to change, he meant it. He believed he could do it, then he fell back into the same cycle that made you want to leave so many times. He's human and he's chock full of drama.

My husband was also emotionally abusive because he grew up with a controlling mother who did that to her kids, so naturally he did it too. The way he argued was a major source of conflict for us because he did all of the classic methods of emotional abuse and I would always call him out on it (which, of course, made him defensive). What made a difference was a few years ago, he came to the realization that he truly had a problem and was not in control of it. He punched me in the face and fractured my eye socket. He immediately regretted it. He panicked and wanted to call the police to turn himself in, but he didn't want to go to jail... He was in a complete state of panic.
I was absolutely pissed off because it was a humiliating position to be in. I am NOT a weak person. I told him to pack his things and get out. In my state, you can't legally file for divorce unless there's been infidelity or you've been separated for 2 years, which I find ridiculous. Domestic violence doesn't count as a basis for divorce unless it results in an arrest (and even then, you have to be separated for 6 months). I was livid.
He moved out and was very depressed. He sought treatment because he realized that he had become his mother and didn't want to live like that. He met with a therapist 3 times a week to learn new coping skills and to identify triggers. Of course, I didn't believe he had changed at all at first. I saw this as a ploy for him to save face.
Then, he told his family what happened and invited their judgement. We were separated for six months (how long it took for me to not want to murder him on sight) before we started meeting together to see if the relationship was salvageable.
I told him how the event made me feel, that I was humiliated and felt robbed of my dignity because of the event, aside from the weeks of physical pain I was in, and he heard me. We started seeing a relationship counselor who worked with us to bridge the way we communicate and handle conflict.
Now for the twist, I have been living with PTSD since I was a teenager, so there are times where I become confrontational (especially when I feel cornered), but I will do things like call the person I'm fighting with by a different name or the subject I'm arguing about stops making sense (because I'm essentially reliving a past event in that moment). So, my triggers and response turned into a trigger for my husband. When he better understood my triggers, he felt more prepared to respond to mine. When I became physically confrontational with him (I mistook him for a person from my past), he didn't respond. When I snapped back to, I needed a minute, but the realization that he handled the situation perfectly kind of hit me.
I wasn't ready for the new him. It was a strange transition because it was unfamiliar. There is a sort of comfort in knowing what to expect from someone, even if you really hate it. So, that actually created a lot of stress for me, but also guilt because I realized that he was trying really hard and I was upset about it. The trust was rebuilt gradually and the coping mechanisms we learned started being used more and he eventually moved back in with me.
We still had hiccups where we'd yell and call each other names, but the difference was this time, we would take a minute to cool off then meet to discuss what happened and why we blew up at each other. I can't say things are perfect, but there's a lot more trust and affection now that we feel there's a deeper understanding between us and that we fully understand each other's triggers. If one of us crosses a line, we have a specific manner that we agreed on to voice those concerns and have both agreed to be open to each other's concerns.

I say all of that not to convince you to stay with your husband but because I think it's really important for anyone to be able to tell when someone is capable of changing their behavior. It takes a whole heck of a lot of time and motivation to change such a deeply ingrained bad habit. It requires that you are very insightful and simply cannot be done without professional help. YOU seeking help for your husband doesn't mean anything compared to him seeking it out for himself.

I know he probably has a lot of good qualities too that you just wish you could have without the drama. That's how I felt about my husband before the incident. Like, I was frustrated that he continued to be an idiot when I just wanted him to see the light and stop being an idiot. I consider emotional blackmail an idiot's game, by the way (hah).

Your son is very young and I think it's worth it to think that maybe you should want to expose him to healthy adult interactions. Maybe your husband would be on his best behavior if you two aren't in the house arguing. No one wants to grow up to see their mom disrespected and treated like garbage. Even worse, no mother wants her son to grow up to disrespect women and treat them like garbage. I think those are all things you should consider when you make your decision about what you need to do for your sake and your son's.

Good luck to you. It's a tough decision either way.