It is wrong from your wife to visit her x-husband. This is not acceptable neither in Islam nor in common sense as he is a total stranger to her.
Divorcing her is something you have to decide whether it was wrong or not. If she insisted on going to him even though you told her not to and you also explained to her that this is not allowed in Islam but she still went on with it, this seems like a typical westerner woman who sees herself superior to her husband and that she is not obliged to obey him. Therefore, your divorce is justifiable.
You have to judge whether this woman has the potential to change into a practicing obedient wife or she will remain an arrogant woman. If she is not willing to change, you are better off without her before you get any children from her.