Although it is very important to be considerate towards your wife's feelings and value her, in such a situation she should respect your request and take it the positive way. She might get upset, but if you communicate things in the right way and share your concerns, for sure she will honour your view.
As Muslims, we do not believe in "free-mixing" between genders, and therefore we do not have such a thing as a "friend" of the opposite gender.
Bearing in mind that you have legitimate concerns that make you feel uncomfortable with her talking to this male individual, and not that you are paranoid or being difficult.
With prayers for your success.