Thumbs up from here, Lara. It is a good plan.
I hope your therapist will help you. What I have learned in therapy (7 years! Those Jungians
--is that current grief is very connected to past grief. You lost your beloved brother to a drunk driver. You don't want to lose H to drugs.
I think 3 months is a good plan. You will still have to consciously surrender to the will of your Higher Power and release your ego's desire to control or to predict. Surrender is the essence of recovery. And though it sounds like weakness, it really does take conscious thought and prayer. If you can find help with this, the 3 months will be easier on you.