Well, better to do something to make her jealous.  Try to ask her about the girl you like for example.  Ask her opinion and tell her you like that girl.  Her simple gesture and temper will give a lead about her feeling toward you, and I think you lucky enough to find that kind of girl.  No string attached.

Try to do something that can make her jealous, if she gets jealous meaning she has a feeling for you and she loves you.

You are the Guy. If you won't have the courage to actually draw the line of  what your relationship status is, the relationship could hardly start and frankly it wouldn't last. Chivalry is not dead and it should come along with an Alpha Male courage to make it continue, which in your situation haven't even started yet. Guys are territorial yes, but girls are way more attached on that part of the relationship. If your woman won't brand you as her own, it says so much about how much she actually want you. I know it's hard, being in a relationship without any label, last year I've been there but I the female and so I believe I can't make the relationship official because my man haven't asked me 'the' question. The only option you have right now as of the moment because the situation is actually affecting you emotionally is to have the courage to actually tell her that you want more than what your getting out of the unofficial relationship you have with her. Ask her if she want to make the relationship official and if she actually want you as a boyfriend. Draw the line, brand her. If she doesn't want that, it's a totally different matter now I guess.