I'm Upset :(((((((((((((((

Okay; so I've been having a rough patch with one of my "friends". so last week everything was fine with our friendship, then today I tell her that I have to talk to her about something really serious; and she laughed at me and walked away to talk to some fat pig. I'm really upset . What i have to talk to her about is sooo serious and it upsets me that she didn't care that i'm sad and everything. what should i do??