Holding your boundaries is a good thing--and I believe that telling him he could live with you only under certain conditions is exactly that, rather than an ultimatum. You offered him an option, and he didn't like the particulars, so he declined. He may say he wants help, but only if he can dictate what that help looks like. You, in turn, have the option of retracting what you said and doing things his way. It's a push/pull until one of you surrenders. If we surrender to what the addict wants, the addict will not get what he needs.
Maintaining boundaries does not always feel good, but that does not mean it isn't the right thing to do. I am proud of you for remaining firm and letting him work this out like the adult he is.