This isn't anything you can fix. Not the alcoholism, not the violence. Being drunk is sometimes used as an EXCUSE for violence, but the vast majority of alcoholics do not become violent. Please call your local women's shelter or the National DV Hotline and talk with an advocate about safety planning. Even if you feel like you can "manage" it (because you've done it before).
Please stay safe and take care of yourself and your child. This is terrible for him, and he has NO say about it.