Very sad. Well, this isn't my style to air my problems, but I think only a graphic example of what your future would probably hold for you with him is the only thing that may help you to make a wise decision.
Having been married to a substance abuser for almost 15 years, I can tell you it's not necessarily contagious, but that doesn't mean that it couldn't be for some people.
Regardless, my advice would be to run the other way, to spare yourself the inevitable pain and heartache of watching someone you love slowly destroy themself. I did leave once for about 8 months. I hoped it would wake him up, be his "bottom" so to speak, but he took a decided turn for the worse, and plunged us deeply into debt by losing his job and living off of a credit card, thereby forcing me to pay the mortgage (house is in my name) and for my apartment. He's been to rehabs, lived on the street and in cars, seen all his friends die, even spent the night in jail once and had to go to court for walking into the wrong house once when he was drunk. Hmmm....let's see, between bail, the lawyer and court costs, that set us back about $2400. I think sometimes only death is some people's "bottom". Not wonderful options, let me tell you...watch someone you love slowly die, or kick them out and hasten the process.
And the kicker? He's the sweetest, kindest, most big-hearted person I've ever met (drunk, high or sober.) But he's a hopeless addict (aside from Divine intervention, for which I constantly pray), which is not conducive to a real relationship.
Make a clean break now before your feelings deepen and his dependence on you increases and before you become financially entangled.
Regret is a bitter pill.