You and Itachi were getting married. The discussions for the bridal party and groom party were going on, and now Sasuke, being your best friend, was being fought over.

"Sasuke will be my man of honour. He's my best friend!"

"He's my brother, so it's pretty much standard that he would be my best man."

"But you have Shisui!"

"But Sasuke is my brother."