Niklos, your original post just described my exact situation about a year ago better than I ever had luck doing myself in here...
I agree with the others that she's just using you as the in-between guy at the moment. What I did was keep being nice hoping that things would evolve as they DID seem to get better (we went from only hanging out while drinking, to hanging out sober like you).
Unfortunately about half a year ago she found another guy, and I was devastated! Even though we were never boyfriend/girlfriend it took me a lot of time getting over this, and damn it if she didn't just tell me a couple of weeks ago that she has actually kind of regretted that she didn't let things evolve between us. Nothing will happen though, because she already moved in with the other guy, but this just set back my recovery over her to almost square one
So my advice is to talk things through with her. Be sure to let her know how you feel about her and how much you enjoy her company and that you'd like things to evolve. If I could do things over I even think I'd have let her know that I don't just wanna be the in-between guy...
Hope things work out to the better