Ok - first of all - he isn't slipping and falling into a glass of booze, now is he? Hon, he is drinking. Period. Call it whatever you will - slip, relapse, temporary insanity...doesn't matter. He is making a choice to have a drink, and justifying it through you and your behavior.
He isn't ready to stop, and this is probably what bothers you the most underneath it all.
"well it doesn't really matter b/c you don't treat me any differently if I drink or don't".
Oh pu-lease. Serious quacking right there. Ignore that. Stopping an addiction to mind-altering substances is what responsible grown ups do. He doesn't get any special treatment for being a freakin grown up, any more than I get special treatment for raising my kids or paying my bills on time.
But he keeps slipping, for me it all starts at point 1 again.
Point 1? Not necessarily - if you mean some time clock gets a big reset everytime he chooses to drink or use. I hope what you mean is you see him not being serious about sobriety, and this is concerning you. And there isn't much you can do about it, because it is his problem to fix after all.
What you can do is find some support for yourself, because this is a downhill ride - fast. It won't be long before he is right back to where he was before rehab. Do you attend Al-Anon?