Don’t show anytype of anger towards the situation, it will only drive her away. If she was a good girlfriend she would stay with you, knowing the last relationship ended for a reason. If she is put into a position were she has to pick between you or the other guy, then you should just leave her. The guys is a dick for thinking he can come and cause problems in your relationship, so don’t let it. If your girlfriend is committed to you, and didn’t want trouble then she should block her ex, because why is she talking to him in the first place. Your not gonna know what him and her talk about, and it’s her ex trying to confess his love so she shouldn’t have him on her phone. 3 months isn’t a long time in a relationship, the same amount of time she spent with him. If she leaves for him, you’ll know she wasent even worth it because in those 3 months she still wasent over her ex. If she stays for you and cuts off her ex, then you better continue loving her. I wish you the best of luck, and hopefully your girlfriend is loyal.