Editor#6
The problem in this situation is not what you should do, but rather what you should not do. This girl is still with her boyfriend, and she will not plan on leaving him until she can find a better option –at least in her opinion. Do not try to be Prince Charming and swoop her away from her boyfriend. This may seem romantic and spontaneous, but it will not give her adequate time to decide who she truly wants to be with (or if she wants to be with anyone at all). If you care about this girl, you should want for her to be happy and confident in her decisions, regardless of whether you are first or last on her list of importance.
Her supposed affection towards you may also seem like a challenge: which guy will win over the girl? It is not a good idea to get involved in this type of situation. Taking on this challenge will detach you from current social and academic life, and this girl will already know who she wants to be with in the end (most likely this will be her current boyfriend). Ask yourself: are you even ready for a relationship? You would have to spend time with her, not your friends, and spend money on her, not yourself.
Being flirtatious is a part of being feminine. It is a way for girls to feel admired and dominant. This girl you like enjoys gaining recognition from both you and her boyfriend, but she is not going to sacrifice her current relationship just to be with someone who “really likes” her. Do not create a fantasy in your head that she will be with you in the future. Focus on all of the positive aspects in your life right now: your family, friends, hobbies, up-coming events, etc. Just remember that, as corny as it sounds, there are plenty of fish in the sea, so don’t worry; you will find that special someone.