Am I wrong for wanting him to stop?

Ill try and keep it as short winded, but as explanatory as i can lol... So Hey, im 26 years old, I have two beautiful daughters age 5 and almost 2.. I've been with my partner for roughly 7 years! We are fab.. we are getting married in 2019! Although we have one problem that seems to come and go... He would like to smoke cannabis from time to time (baring in mind he did use to be an addict too) but ever since we had children, I have 100% never wanted it.. I never particularly loved much about it before being pregnant.. but even more so since starting a family. Our first daughter was actually a shock pregnancy.. And I was very upset and scared to begin with.. as I knew I didn't want to be with someone who smoked or took other recreational drugs.. I said this, And I was lead to believe that the pregnancy was a big kick up the bum that he needed and we would all be okay.. well 99% There's been no problems in that respect.. but the last few weeks we have been going round in circles, as he wants to be able to smoke it from time to time... after hours of discussions, we compromised that it would be once in a blue moon and it would never come back to me and the kids.. however with in 9 days it had happened a couple of occasions, And I had already found it in the wash.. so to me.. i feel like this isn't going to be 'once in a blue moon '.. Also what is hurting the most is that he will admit he can live a happy life never touching it again, but will still choose to want it again.. And I feel like am I, are we , not enough of a reason , to think ' fuck It ' to something that apparently means nothing to him? So anyway.. I feel a little lost as what to do...

Once a pot head, always a pot head. Trust me, talking to your partner won't make him quit, been there done that. 2019? It's still 2017. Chances of this problem escalating is at a high percentage.

Yeah our wedding is already booked for 2019. Don't get me wrong, he's not been smoking all day every day, and he says to me that's not what he wants to do.. but I'm scared that if I 'allow' him to occasionally smoke, It will gradually get more and more... Am I hypocritical because I don't mind him having a beer from time to time?