Friends Don't Always Last

I try to be nice, but you just laugh. I'm not fitting in anymore, what can I do? You don't realize, but it's starting to hurt. When everything's just right, it always turns to dirt. Help me, what am I doing wrong? I don't understand, I'm there when your not strong. I try to be happy most of the time, but it's getting harder now, knowing your friendship isn't mine.