My heart is with you,
Aside from being supportive you can also get rid of, dispose of, or hide any triggers that might cause relapse of whatever substance he was using, this means that anything that made him want to use/drink get rid of. An example for a smoker is to throw away or hide all ashtrays, cigarettes, cigarette boxes, paraphernalia etc. Situations or places that led to using/drinking etc should also be avoided. This part is also especially hard but if there are particular people or individuals that trigger or would lead to a situation of relapse should also be avoided, even if it is close family or friends, for a while they should not have contact with him whatsoever.
As far as other methods I would look into Reiki healing, it helps not only with physical injuries, ailments, and pains but also with psychological, chemical, and emotional illnesses as well, in this case chemical dependence that is followed or tied with both psychological and emotional baggage as well. There are many other healing techniques as well including massage therapy, Acupressure or puncture, aromatherapy, meditation therapy, hypnotism etc.
My prayers are with your partner, you, and the ones around you. I will make a prayer flag and burn it in a healing ceremony tonight. I wish you all well and the best of luck and healing.
Brightest Blessings, and Peace be with you, Stay safe and be well,