Am I wrong?

I know when you live someone and have promised to marry them you are supposed to stay through the good and the bad times. I know I should keep reminding myself this buy I feel like there has to be a limit to this rule. My fiancee has a drug problem. They say weed isn't addictive and doesn't do harm but that's bullshit. He's a different person when he can't get it and I'm tired of trying to keep the peace like I'm forced to enable him or I don't love him. I have put myself in debt and it's no end. I am spending more than 100 a week just on his weed. I'm tired and I don't think our love will survive me losing respect for him. I don't understand why he's so weak why he can't just quit and why he has to be so selfish. Am I wrong to resent him sometimes?

Update: I don't think that our relationship will make it through this at all. We talked about it and he admitted that he has a problem. Yesterday he smoked only twice and then today he decided to not smoke. It's 8 pm he has been angry and mean all day he won't eat just quiet and moody but someone he knows agreed to let him hold some until he gets paid now he's all happy and normal. I don't think that he will ever stop he is only happy when he has it. I feel like he's weak and I'm starting to lose respect for him. How can I marry a man who has no self control and who values a drug over me?