Give up. She has moved on. It is time for you to do so as well.
If he has a girlfriend, don't go back. He will do the exact same thing to you, that he will have to do to his current girlfriend. Good Luck!
You don't.. you wait for him to regret how foolish he was, and come back to you. If not, then it wasn't meant to be.
you already answer that to your self
Choose between them, if you left your ex for a good reason then continue dating your new girlfriend/boyfriend.
get over it
Does she have another boyfriend? If she does you can embarrass her in front of him. also you could get a new girlfriend if you don't already have one and show your ex whats shes missing. but shes single and jealousy is just rude
If she was real, she will not become an ex.
You don't ! Your relationship with him failed for whatever reason. He has a new partner - you have no right to interfere in their relationship in the hope of winning him back !
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.
maybe he wants you back.
Simple Answer: You don't.
show her that you loves her more than her new boy friend and point out all of the bad things about her new boyfriend