She can smell you're ready to give up an arm and a leg for her from a mile away. Sure, space may help the situation, but that rarely helps on its own. You giving her space means very little when and if she requests your presence, you'd be willing to be there in an instant. And what is the point in making you romantically exclusive, if she can enjoy the benefits of your friendship and little to none of the commitment? If love was purely transactional, which it isn't but still, I'd say you're bringing about a very poor business proposition to this girl.
What have YOU done that other guys haven't done (or aren't doing)? Why is it that men don't ask this question more often?
If we establish the premise that people want what they can't have, then you need to be The Guy that other women want. So you need to go out there and date and give off the vibe that that is the case. Living in abundance will affect your life positively. You can still care about this girl, but you do not make her a priority. This, bizarrely and yet unsurprisingly, will rekindle her interest in you (it is still your job to demonstrate to her why she should stay with you long term, though). And if what you had was actually your chance to bring that in her and you got what you're bringing to us now, then move on. You simply can't strategize your way into a relationship.
You have to evoke that in her. Love is real, but it isn't spontaneous.