Your doing the right thing buddy. I have been with my girlfriend for 3 years now, so I like to think I have learned a little something about the mind of a women. Not a lot of guys understand this, but girls are just like us in many ways. One of them being that they do enjoy have friends and they do enjoy "Bro Chillen". I know sometimes me and my girlfriend both get that feeling like gosh we wish we were single. Not because we want to go out and hook up with other people, but because we both need time to ourselves here and there. So when that feeling comes up, we walk in seperate rooms and do our own thing for a while. Of course later we need/want the attention from one another and we hang out.
So like I said in the beginning, You are doing the right thing by giving her space and letting her understand you trust her and are first and foremost her good friend.