I'm going to miss my brother's wedding
Why are you going to miss his wedding?
I just don't think I'll enjoy that very much.
It is an important family event! You should do your best to make it. It doesn't matter if you will enjoy it or not.
I'm sure my brother wants me there, but I still don't want to go.
I understand that you are allowed to do what you want, but I'm just letting you know that it's expected that siblings attend each other's weddings. I still think you should go.