*For lack of better terms, we can assume "ex" includes a boyfriend through anyone you've had a thing with that was upsetting when it ended, and "new girlfriend" is the girl that boy is now having some type of romantic interactions with.*
The worst thing about a breakup (besides the typical heartbreak and gaining thirty pounds from ice cream consumption,) has to be your ex-whatever finding a new girl. He may not be dating her, and hey you maybe never even dated him yourself, but it always sucks to see someone you had feelings for sharing those feelings with someone that isn't you.
When this happens, the overwhelming reaction seems to always be a complete dismissal of the new girl. She's always uglier than you, less smart than you, her left leg is a little longer than her right, or whatever other things you point out to make yourself feel better about the fact that he's definitely downgraded.
But what if he didn't?
Now, boys do for sure downgrade sometimes, and sometimes the new girls they find themselves with can be spiteful and rude. BUT, humor me for a second and take a step back. If this girl wasn't associated with the boy you liked, would you hate her? Is she really as petty and ugly and horrible as you've made your friends repeat to you that she is?
Probably not.
Here's the thing. It's okay if the new girl is completely amazing. It does not make you any less amazing or valuable or likable at all. Even worse, it is not this girls fault (most of the time) that you two aren't a thing anymore, so why do we find ourselves being so angry at her and not the boy that broke our hearts?
Girls are always talking about girl power and females hyping each other up, so maybe, just maybe, we should do that every once in a while. If you want to be mad at someone for the new relationship, be mad at him, because honestly you and her probably have a lot more in common than you think.
And hey, that guy sucks anyways, so when he breaks her heart too, the two of you can be great friends.