So you find yourself in a blended family with stepchildren, some who are grown up. By no fault of your own, one of the stepchildren happens to become a drug addict. You and your partner are non-drug users, not alcoholics and never have been. You are both "Normies" (normal people who do not alter their state of being by getting high or drunk all the time, preferring to mentally keep it normal).
I am the Mother of an Addict learning more about addiction and recovery every day. One of my adult children is an Addict who thankfully is in Recovery (a Rehab program) right now. My daughter came into her addiction via a broken bone that had to have surgery and pins put in it. The surgeon gave her a “lovely”pain management prescription for Norcos. She got a 90 Day supply given to her by the surgeon, and then when she had taken all of them within the first month, the doctor authorized a refill… TWICE in that same 90 day time period.