Oh boy, I'm really sorry that he's relapsed like that, and as well, I'm sorry that you are dealing with it. Very sorry.
Do you have anywhere you can go? I know you say he's supporting you, but do you have family or friends that you can stay with, move back home?
He needs to do this on his own, and I hope he does.
I relapsed, but I'm back and it didn't even get bad either. For me it just got to the point where I got to thinking "you know where this is about to go 'Vegi'..." so here I am. Have you asked him what it was that made him get sober the last time? If it was really, really bad?? If so, ask him if he wants it to get that bad again, as a reminder...
My thoughts are with you, hope you get some answers here, welcome to SR, this site is awesome. :ghug3