As an adult, he may make bad choices but they are his to make.
Us trying to support / control another adult's actions is pretty much doomed to long term failure.
I know for me, supporting and providing a "safe, comfortable space" for the alcoholic in my life, just as you did,
simply gave them more room to go off on a binge and still keep the idea that they didn't have a problem, i.e. the idea of "a normal life".
That simply prolonged their (and my) descent into addiction hell.
What I would do now, after learning years of hard lessons,
is to step back and respect yourself, and the addict enough to let them make their own choices.
Becoming sober, if he's serious, is truly a full-time job and is his to do.
Tell him after he is sober for a year to look you up.
Don't wait for him, but if it is meant to be it will be
but only if he steps up and takes charge of his own recovery.
Best of luck to both of you.