I'm going to leave my best friends wedding
Oh no, why? Did something happen?
I just feel watching wedding makes me sad, I don't know
It's not very nice to leave in the middle of a wedding. You should just leave as soon as it's over instead.
I still want to say goodbye to them but I'm bored at wedding, what am I currently doing?
It is your best friend's wedding and they are expecting you to be there for them. If you leave early, then they may think that you really do not care about them and would make them think that you do not really care for them as a friend. I do hope you stay and mingle with the people in the wedding so that you would get to know the other people in your best friend's life.