I don't want to wear a suit jacket to my brother's wedding before his fiance dies
Where is your brother's fiance now?
She moved away, and my brother was just informed via email that she is dying.
You really should dress formally for a wedding. If you don't want to wear a suit, don't go. Respect your brother's wishes.
It's not that big of a deal and plus she is not close family. I have an appointment to get my pubes dyed, need to go.
Just because she wasn't close to you doesn't mean she didn't matter to him. He is going through a difficult time and can probably use your support. Even if that means just being present at his wedding.