You get to be the one who made rainbow cake with them or first showed them Arrested Development or whatever made your relationship special. Men, by nature, are very protective of their women so I guarantee you that to the new boyfriend you trying to get his girlfriend back is going to paint you in a light where you are an enemy. For example, "Remember when we went to that great restaurant. Your ex's new significant other is not your replacement. If it is the other case he soon will fade down and probably contact you or try something to get your attention. Providing emotional support for your ex girlfriend when you become friends is really where you are going to shine.
My Ex Is Seeing Someone Else During No Contact
Imagine that your new made up girlfriend is best friends with her ex.
How To Get Your Ex Girlfriend Back If She Has A New Boyfriend