Well i don't think that you can really do anything about it. But if you really want her back that bad i would say just try talking to her. See if shes happy in the relationship shes in. If she says no then just try showing some interest and maybe she'll take the hint. If she says yes then you need to move on or just wait for her. But trust me don't try and sabotage the relationship that wont get you any where because if she catches you, you wont have a chance.
She probably did it to make the ex- boyfriend jealous.
You should be confronting your ex and telling him you do not like his girlfriend asking your children about your new boyfriend and if it keeps up he will only be able to see his children at your home or without his ex girlfriend.
you should find a new bf
A girl should never fight with her ex-boyfriend's new girlfriend. The girl should move on and let her ex and his new partner do the same since fighting will not solve anything.
find a new boyfriend or girlfriend to stop you thinking about them ( your ex )
You do absolutely nothing about your ex boyfriend considering he has a new girlfriend. If he loved you he would break up with his girlfriend and since he has not then he wants to be with her and you need to accept that. Just because you have broken up with your boyfriend it doesn't mean you can just step back into your ex boyfriend's life.
Simple Answer: You don't.
To say: "Just to let you know, I dated this girl before you; but we are through now"
It means the ex boyfriend still likes the ex girlfriend.
Let him have a threesome with your sister (only if hot)
If he has moved on and has a new girlfriend it is time for you to realize it is over and move on as well.
Like the ex boyfriend? Okay that means she really likes the ex bf.