"I want to be the cool girlfriend / wife who doesn't get mad when he talks to other women."
...That will be easy enough when he respects your wishes to end communication with his stalker friend. It doesn't look good to tell you the truth. If you are out to dinner and see an ex-girlfriend or a current co-worker and he says, "hi," I have a feeling that you wouldn't mind so much. A frequent visitor to his home, when you aren't there, while you and he are fully aware of her intentions is another thing altogether. It really isn't appropriate and, in my opinion, you shouldn't be upset you have the reaction you do.