TTC and selfish fiancé

Hello group,
So, my fiancé and I are trying to conceive, and my gut tells me that I am pregnant, although I am waiting a few days to test. When we started TTC, he promised to give up weed, and cigarettes. Today when I came home from a job interview, the house reeked of smoke, he told me, "oh I smoked some pot in the backyard I hope it's ok"
I was sad, and he noticed so he stepped outside and hasn't been out for a couple of hours or so.
Look, I don't have a problem with weed, but it is illegal here! My fiancé already has a DWI that he got in college, during grad school. Now I would like him to step up and prepare for fatherhood what should I do
Ty