For me personally...
I begin a relationship with a certain frame. And I keep it going strong. Part of that frame is no drama and no control / jealousy issues. I have friends that are girls, I text them, I'm friends with them on facebook, and it's not changing. An outsider looking in might even think I'm flirting with them. And that's not changing. What I promise is that I'm not hanging out with them behind your back, and that I'm not cheating on you. That's it. If you expect me to go any further than that, then it's not going to workout. And in return, I don't give her shit if she is friends with guys. As long as she's not going out behind my back or being over the top flirty, I don't give her shit about it.
When you start a relationship with this frame, you set the precedent and any complaints down the road you have the response of "you knew what you were getting into, I made it as clear as possible. You're a big girl and you make your own decisions. I'll give you a night to sleep on it and tell me what you want to do tomorrow".
I've yet to have a girl break up with me because I was friends with girls or even because I was flirting with other girls. When they do bring it up, and they almost always do, if you keep the frame then they have no where to go.
I'd honestly not even reassure the girl that I wasn't hanging out with other girls behind her back. But all of this depends on the girl. Most PUA tactics are geared toward high status beautiful women. Some shy family-oriented HB6 will probably require MUCH less maintenance than the HB9's.
When I say behind her back, I mean I'm not going to tell her that I'm at work and really im hanging out with some chick. I'll hang out with the chick, but if my girl asks I'll just be honest about it.