First I am sorry that you continue to deal with his drug abuse issue. And I am more sorry that violence has played a part in your lives. I agree strongly that you should reach out to a domestic violence hotline in your area and begin talking with some professionals. I also believe that you would benefit from al-anon or nar-anon.
Reaching out to his brother I’m sure came as a relief to you, it’s always nice when we can share “the secret” as it tends to not own us as much. But his brother is not the magic bullet nor can his brother make his stop using. And a week away will give you just that, a week with out him physically present but he and his addiction will continue to occupy your every though. You may want to start thinking long term here, the last time 6 months away from him sounded like you were physically away from him but still very much emotionally attached and interacting with him. Something has to change and the only possible person in this equation is you, the one you do have control over.
Can you go stay with family or friends? Can you afford to be on your own? And if not, what will it take and how can you bring that about? Rather then focus on HIM and what HE needs to do for HIS addiction it’s time to start thinking about YOU and what YOU need to do for YOU in order to survive and thrive in life. And none of that should be DEPENDENT on what HE does or says or claims he will do. He’s had 2 years now, how many more years are you going to give him?