Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I am very sorry to know about this shocking situation.
Drug addiction is one of the toughest issues deeply undermining a person's life, from the personal to the family level, nothing could be immune to its devastating destructive power. Unless the person truly happens to acknowledge his addiction as such, as a chronic illness, and commits to his rehabilitation process without excuses, taking full responsibility for his choices and actions, it would be hopeless to expect his personal or family life to heal and develop as healthy and fulfilling realities.
Denial, secrecy, avoidance, justification, control, manipulation, dishonesty and more are at the core of addictions, and they fuel every form of neglect and abuse, and as long as the person does not truly take full responsibility for his reality, he would continue to perpetuate and deepen the addiction and the dysfunction he creates with it. I have to say that that most times people presenting serious addictions, do use to have serious mental health and personality issues too, which fuel and enable the addictions, and from there further abuse and neglect.
Thus there is no way to effectively cope with a situation like this but by setting clear and healthy boundaries and limits, in order to protect yourself and your child. He is not a victim, he is an adult and the only one responsible for his choices and actions, and he is telling you this clearly and directly, that you nor your child are a number one priority in his life, that he chooses to stay with his brother and friends as he pleases and that you cannot say anything about it.
Please look for all the help you could get from your support system, namely, those healthy and caring family members and close friends, since this is tough for anybody in your shoes to cope with, and seriously consider professional counseling support, for you to get the tools and professional support, to take good care of yourselves, without exposing to further abuse or neglect.
Does it make sense?