One thing I made clear when I started a relationship with my now-ex, was that I have female friends and don't intend to drop them, and that I don't mind her having male friends - i.e. let's do what you're supposed to do in a relationship and trust each other.

It was early enough in the development stage to set 'ground rules' like that (and without actually saying so, make it clear that I'm not interested in anyone who's going to break any of my friendships)