OP is starting off the Marriage by demanding - not asking - that the Best Friend not be at the Wedding at all, not even just asking (not demanding) that they aren't part of the Wedding Party.

I'm saying that clearly OP and the Best Friend's relationship is gonna get better, OP is gonna be Toxic around Best Friend and make comments about them, and could potentially demand Fiance cut Friend out of their lives completely.

I'm saying, don't even bother getting Married if you such a problem with it. Why would Fiance be okay with ditching the Friend after just making Friend part of the Wedding Party?

The choice is "get rid of your best friend. Also it's not a choice, it's a demand" - that's what OP wants. So why even bother going through with it? Is gonna be happy cutting off his Best Friend? Is his Best Friend gonna be happy to be not only kicked out of the Wedding Party but excluded from the Wedding entirely?

How is that a good start to any Marriage?