Like I tell my kids (one of whom is 13) when I leave the house. "You don't answer the door for ANYONE -- I don't care if it's GOD. You do NOT ANSWER THE DOOR."
I don't need to make them a LIST of who NOT to answer the door for. EVERYONE is on the list. Even God.
Lol. This is almost exactly what my son hears (and always has) and that's how I keep him safe. He's around OP's stepson's age, and in our case, he just knows it's a mom rule and never equated it to anything else.
In our case, it's a little more complicated, Dad is not only a bad alcoholic, but he's quite abusive with a long history of abuse (last incident - tried to physically attack me in the middle of the Courthouse with Court going on) but, through any and every incidence, my son has known minmally anything that occurred (and he never heard anything from me first). I give OP a little slack for telling the son anything, not because I think it is the best decision, but because it is a hard situation to navigate through. I just find that the more the child knows, the bigger burden on them because they don't just worry about their own safety, they worry about yours and that's too much burden on a child.
My personal 2 cents is that at 13, there's no need for an adoption. They know who their parents are and I think the benefits of having both biological parents and step parents is just more people to love them. It's not my place to define or interfere with his relationship with his dad. I keep him healthy, safe and emotionally well and that's my job. I just tell him his dad loves him and has some problems and sometimes grown up problems get in the way of all kinds of relationships but I don't have a crystal ball (and neither does he) so maybe in the future things will be different, etc.
With addiction issues, it often never improves, but sometimes it does. And that's why even after 4 months you can file for abandonment, it's rarely granted if contested. Most adoptions and termination of rights go through only if the other party doesn't really contest. If there are conditions on visitation like OP and mine, courts here rarely consider the lack of visitation as grounds for abandonment. They really like to err on the side of caution, which is a good thing when you are dealing with something so permanent.
Also OP - the cell phone - I get responsibility,etc. but for safety concerns, buy this child a cheap prepaid phone and put it only the numbers he can call. If he loses it, you won't be out much money. When you have safety concerns, I think it's important the child has one (or a tracking device as someone else suggested).