It is not only common but almost downright programmed in her brains for a girl to hate on her significant other's ex ("SOX"). After all, that bitch had sex with your man!!! 
Do you have anything good to say about your SOX?
Don't you think you are younger, far prettier, smarter, better grounded, and more successful?
Don't you ever wonder why he's going out with her in the first place?
But similarly, I believe the ex somehow dislikes the "current" for the same reasons too. Be it just a self-esteem problem or not, those feelings are far more real than ever. They are there, alrite.
He went out with her a couple of months after we broke up. I, was of course furious and devastated when I found out. I did know how of her existence previously. He wouldn't disclose anything about her, or of any potentials. He still doesn't.
I would look for hints of her being at places he's been. In his car, in his house, his bedroom... and everywhere else possible. Maybe a plush toy here, or some photographs there, or whatever at all. Underwear, sleepwear, notebook/laptop...whatever. When we used to be dating, he had stuffs over at my place, and I, certainly did, his...
But no, I could not spot anything around. Not even till this day. Except for some ticket stubs from the movies, perhaps. But despite all that, I could feel her existence. But being me, I really needed to put a face to the name. "The girlfriend" just doesn't cut it. I disliked her, down right hated her.... for obvious reasons. And I guess I needed that face, so that I could picture myself aiming darts at her.
Until one day, I was talking to his close friend, and she disclosed something unexpectedly. They were all at a friend's place, playing cards during chinese new year. The "current" was there... just like how I used to be there. And out of the blue, she said "I can see that she's really in love with him. He's a lucky guy. For he's got two girls who love him so deeply."
And I was stunned. Caught speechless. Tears rolling down my cheeks as I feel as if my heart has just been stabbed multiple times. I just stood there, unable to digest what I just heard, and unable to move for a good few minutes.
And then it hit me that she was no longer the enemy. I might not like her, I still don't. But I can't bring myself to hate her. Despite my prejudice against her, I realise that we actually have more in common than I imagined. We are in love with the same man. We see the beauty in him. And I'm sure, he somehow, sees the beauty in us too. I was in her shoes, or rather... she was in mine.
In this game of love, there have been others before me and, for certain, there will be others after me. I have no control over the past nor do I have the power to manipulate the future. But for what it's worth, I had my time. And they were real good times... Times that he might have let go of, but I hope, those times will remain at least in his heart... forever.
As for me, I've finally let go of the hatred for her.
Look at the chocolates on display for sale.... Don't they all look pretty??
Met up with them @ Marriott Hotel, where they were staying. And then headed to the city to do some shopping since it was a Friday night. :D And the "end-of-summer" sales were so good, that she just couldn't not get something. Heheheh..We didn't even realise that we were that hungry, until I looked at my watch, and it was already 9pm! 
