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 its starting to hurt,
when every-thing's OK,
you treat me like 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 its getting harder now,

Knowing your friendship isn't mine.