What should I do...

My fiance and I have a baby together and he's only 3 months old. We do love each other but we have some differences we've been trying to work through. Despite our differences though we've been trying to make it work for the little guy because i personally want him to have his father.

Now i know a lot of people out there love weed and i know it's legal and truthfully I know there are a lot worse things to smoke... But personally, I dont want it in my life. I have my reasons but I have told my fiance several times where I stand but he constantly has gone behind my back and lied about it...

Not only that but his best friend has been a toxic shadow in our relationship. His friend is 29 and is jealous of where my fiance is in life and constantly tries to make him leave so that they can hang out more and party again.

Well my fiance and I finally talked through everything and we actually almost broke up. But HE told me that he would quit smoking, stop hanging out with his friend, and that he would try to be a better more productive person.

....Less than 24 hrs later he goes and smokes with his friend again...

Should I give it more time before I can really judge the situation or do you think that is a bad sign that he already couldn't control himself?