Mmmm, for someone that was fairly relaxed about what happens NYE, you seem just the opposite.
If you have asked him to stop doing weed, and not only has he not, but he has asked his mates over to join in, it indicates to me, he is not ready to quit. You need to be realistic about this and decide if its a deal breaker for you or not.
But if he is asking you not to drink, thats a fair response, again you need to decide whats important to you in a relationship. Why is that fair, well this is my rationale:-
While being intoxicated with weed feels different than being intoxicated with alcohol, the two have roughly the same effect on your cognitive abilities, reflexes, and judgment.
Both can also leave you feeling a bit worse for wear the next day, though this is more likely to happen with alcohol.
Alcohol has been part of our culture for years (we used to drink it instead of water because water was unsanitary), so there is lots of research/history about its affects.
Weed, well this is becoming more acceptable even in my short lifetime but there isn't as much longterm research as to the effects.
So on balance, I think its a fair response, if you want him to quit weed, you need to quit alcohol!
And lets make it clear, I have never done drugs but I do occasionally drink so I'm not pro drugs, but he has a sound response.
But that is NOT what this is about, this disagreement appears to be about him making plans without consulting you and potentially the host (although that does not seem to be your gripe).
Celebrating the anniversary of your engagement is not a thing, you know that as you wouldn't have been so laid back about what the initial plans were for NYE.
You are miffed you weren't consulted and quite rightly so. This is a learning curve for the relationship, in that you need to run things past each other as you are a couple now, and we all go through this. This type of learning curve generally comes before the engagement though as your needs, wants and consideration for each other should generally be aligned for a marriage to work.