If he is actively suicidal you can call the crisis team – dial 111 and it’s option 2 (it will be something about someone in mental health crisis who is over 18). Alternatively you can ask the police to do a welfare check on him as he doesn’t live with you and say you are worried about his state of mind/can’t get hold of him etc.
Unfortunately, when someone has addiction and mental health issues going on, the mental health services can refuse to deal with that side of things until the person has deal with their drug addiction via the drug and alcohol services.
My addict (partner – soon to be ex) has developed terrible mental health issues since becoming addicted to cocaine and now freebase cocaine (like crack). He has tried to kill himself more than once and one of these times was nearly successful. He had constant agitation, volatile and unstable moods, aggression, severe paranoia etc.
Because the suicide attempt that was nearly successful put him in hospital for 24 hours, he got eventually put on prescription drugs for his mental health… but this is because he had never admitted to health professionals about the drugs or his addiction. He really needs help with his addiction but he will never get it until he has totally hit rock bottom and is prepared to admit what he does and the extent of it.