Friends Don't Do This. Right?

Is it wrong that I'm upset over a friend suddenly becoming friends with one of the girls my ex-boyfriend slept with when were together?

The friend and I used to be really close. We were best friends until she moved to California, then when she came back to NC, I was getting ready to move to Arkansas. And as people do we drifted.

But she was there during the whole ex-boyfriend thing (I dumped him last December.). All two years of it.

This girl made a point of sending me photos and flaunting the fact that he was fucking her behind my back.

There hanging out today. Actually, right now.

And I'm hurt. And a little pissed.

Am I horribly in the wrong?