Most Helpful Guy
She's clearly jealous and possessive and she doesn't like the idea of his ex hanging around in the background. I'm sure you might get a little concerned if you had a boyfriend who was still attached to his ex. You might be more reasonable about it but you'd likely have at least a tiny bit of concern.
He has chosen to be with this girl and he continues to choose to be with this girl. So clearly she is somewhat of a priority to him, despite her causing trouble for you. You might want to consider leaving them to get on with their relationship. He's your ex for a reason.