I've been hanging out with this HB8.5 for a while and, well, she has a boyfriend. I've been gaming her nonetheless, creating immense sexual tension using tons of cocky comedy- I accuse her of seducing me, having a dirty mind, trying to get into bed with me etc. (you know how it is

). Anyway, at one point I convinced her to be friends with benefits with me (best..situation..ever

) but at the last minute she had a moral breakdown and decided it wouldn't be fair to her boyfriend (damn!!). She has told me several times that she thinks I'm hot, we text and joke about taking a secret trip to Hawaii and her texts get pretty hot and heavy. She even told me that if circumstances were different she would definitely go on dates with me.
So recently, being this last weekend, we went to the movies - which I know is a bad setting for a date, but whatever. However, we had to go with other people, including her brother, so that she wouldn't feel guilty. She was the one that suggested the "rendez-vous" and was all over me from the get-go, in front of her brother. I'd push her away, ignore her a bit, pay attention to other girls and her brother (who, incidentally, is the funniest kid ever) and we ended up sitting next to each other in the theater. I received tons of IOI's- she would stretch her back thrusting her breasts forward, mirror my movements and we had intense eye contact (oh, and she was laughing. A lot.) I eventually asked her if she wanted to kiss me (mystery's kiss close), and she freaked out. She backed away (our faces were originally only about half a foot away from each other, give or take) and I told her I didn't give her permission, blah-blah. I froze her out for a bit and later we got comfortable again. But nothing happened. She later reaffirmed the fact that she has a boyfriend (as if I forgot or something

).
My question to you, is what the hell is up with this? Her body language and IOI's suggest she wants my body, but her reactions are always resistant; I know for sure I'm not misreading her signals. She sets up all of our get-togethers, knows we have tension between us and that we're definitely not just friends, but is hung up on her boyfriend. How can I advance, all things considered, and is this even worth pursuing?