Most Helpful Guy
Stop stressing yourself over the other guy, or any guy in her life, for that matter. He's an adult and wants to be with the same girl as yourself, and as I understand it, that makes him your competitor. His goals are in direct conflict with yours, thus his happiness in the matter is a conflict of interest to you.
That being said, she sounds like a user and a manipulator, but given the unilateral details of your post, that's an unfair assessment. If this guy is aware of her disinterest in dating him and yet continues to invite her places in addition to paying her way, then he is enabling her. In this case, perhaps spending time with her his a consolation prize as the result of his failure to legitimately catch her.
Nonetheless, she can do whatever she likes, she is not obligated or committed to anyone. Thus, if she is sleeping with this guy, or that guy, or using him for companionship, she is not committed to anyone
In closing, If you are to land her, you will do so playing her many games. After a year of being aware of your feelings of her, it's safe to say that she should be passed giving you hints and such. And yes, it does sounds as if she is giving you hints to pursue her. However, given her past, I'm skeptical that she would the quintessential girlfriend that you seek anytime soon.