Our stories are very similar. I lived with my ex fiancé for a year and I share so many similar events with you.
I remember going out to dinner with him to celebrate our anniversary and the night being a disaster. A silent and calm restaurant and the drunk guy making a mess, bothering the other couple eating peacefully next to us, drunk-driving after I got pissed and the name-calling directed even at my family who cared about him so much. After all this he stopped at an open bar and left me in the car waiting for more than 30 minutes, so I called a cab and went home knowing he would come back and things would go downhill again. Another night he was drunk driving again and I was scared and started an argument, so he stopped by the sidewall, dumped me there in the middle of nowhere and left home. Thank God there were a few taxis nearby and I could pick one. Never forgot the poor cab guy that calmed me down: "you can do nothing about him. Why do you wish this life for yourself". I wanted to die, felt it was my fault every single time. I feel so so sorry for what you've been through with your little boy because I've been there.
I'm sharing this one incident so you can see you're not alone with your sad experience, and even if I'm still speaking from a place of pure pain right now I say to you they just can't control. And they won't stick to their promises, I believe because they can't.
Don't listen to promises anymore. And don't beat yourself up for feeling bad but don't believe you're the bad one because you aren't. You can't make him change.