Very few women will willingly marry a drug-addict...I think you know what to do...
It sounds lame when you're in the thick of it...but in time you will feel better, your situation will no longer look so bleak...get well, give her all the time and space she needs...this is how you show her that you respect yourself, and that you respect her decision. That's why it's so hard do do that...it requires strength...it's the right thing to do...exactly what is attractive in her eyes...
You'll be ok...virtually everyone has to deal with this kind of thing sooner or later...virtually all relationships come to this position on some level, and how you conduct yourself now, has everything to do with how it may turn out...some guys remain single their entire life, because they can't resist the temptation to grovel like a whipped puppy when his girl draws away from him...
Drugs mostly fuck up relationships reliably...like clock-work...
Best wishes.