I want to go to my brothers wedding even though my wife told me not to
Does your wife have some kind of issue with the bride or groom? Why would she keep you from your brother's wedding?
My brother is my only sibling, so why should I not be allowed to go?
I think it's wrong for your wife to try to keep you away from your only brother's wedding. You should try to find out why she doesn't want you to go and hopefully you can work something out.
I don't care about her reasons. I want to go, so I'm going.
A sibling's wedding is important and you should attend if you can. Unless you're leaving out a big detail here, your wife is wrong and I think you should go.