I think the direct questions you asked me were answered already; at least, they were answered in the way that I would answer them. Addiction to a substance doesn't really vary based on whether the substance is legal or not. Those are man made rules. Addiction is nature. The two are unrelated, only to vary by the degree that society accepts them.
As far as being on subox, I don't have experience with it except in an employment environment. Technically, subox is a recovery drug and part of a recovery process. Folks who are in drug recovery are protected by the ADA. Which means they shouldn't be fired from a job for the use of the substance and if prescribed accurately, the drug should not cause any of sort of inebriation. It in theory restores normalcy.
Again, that is law, not always reality. Patients communicate to their doctors what milligram feels normal to them. So the addict is essentially in control or has influence over their dosage. The ones I know, feel comfortable at a level that causes some sort of inebriation. If it didn't, the addict wouldn't be so hell bent on taking it. It would be like taking a vitamin if the addict didn't have some benefit. In my opinion, opiate replacement isn't recovery. But that's just my opinion.
You have a child to take care of. Why try to take care of someone else too? This person will eventually put you in a situation where you will have to choose what is more important. Your relationship with a man, your relationship with your child, or your general care of yourself. Sustaining as the caretaker of essentially 3 people will leave you drained and disdained.
If he's wonderful in your eyes now, he can be really wonderful a year from now when he may have his life under control.