On the receiving end of a lie

Hello, I am currently a year and a half into a relationship of whom I fell in love with straight away and I still am. Before I start I should probably say one thing, smoking. I have been brought up in a family where smoking is morally wrong and I 0% intention of ever trying to smoke because I have seen the effects. I have tried changing my views but its impossible as it is hard drilled into my brain. So back to the story, when I first hooked up with my girlfriend she was going through a rough patch where she smoked for several weeks, I don't know the full extent. But when we got together she knew how I felt about it and said she would stop. Over the course of the next 7 months she occasionally did it and told me until it got to the point where it was around 8 fags in one night and that is where I told her I can't do this any more, so she 'agreed' to stop. So up until now she didn't do it until I found out yesterday that several weeks ago she had a few and didn't tell me. Obviously I am more hurt about the fact that she lied to me and I feel she is still lying to me even after I have asked to clear things up to start with everything out in the open again. Personally I cannot describe the pain I go through when I know she is smoking when I'm at home. Now she is on about smoking weed with friends as well using the term 'occasionally'. I am struggling to deal with the deceit at the moment and I don't even know what to do. Can anyone give me some guidance please?

If you really are that strongly against it. Then you need to tell her that and tell her you can't deal with it anymore & if she continues that's going against her repeat for you and you have to leave her