Just one thing you should be prepared for. When you tell him you are DONE, there's a good likelihood he will suddenly "decide" he wants YOU, and only you. You may get lots of tears and promises--that he's seen the light, he knows what he stands to lose, he's a changed man, he will make it all up to you.
I'd strongly suggest that if you decide you are DONE, you remember that you will likely hear those things and be prepared to kindly tell him that you wish him the best with his recovery, but you are out of the picture. Telling him this while he's in rehab will allow the counselors to help him process it. His sobriety, and his ability to accept the breakup, is completely up to him.
Some time away sounds great.