If you tell him you won't leave him unless he goes to detox/rehab, and he goes, but then starts drinking after he gets out (which is probable IMO because he was coerced into going instead of being ready to go himself), what will you do? Will you leave then or stay because he "tried"?
I guess I feel like offering him the rehab plan is just prolonging the inevitable, and that it's time to focus on you and what you need to have a peaceful life.