Dude, I can tell you right now that I can relate to this to some degree. I wish I had seen this a little earlier because it appears as if you've already started reacting sporadically to the stress and pain of the situation. This flurry you just had with your ex will be one of many of you two keep doing the things you are. It could be because of immaturity and will happen inevitably, or it could be because you are not being clear and honest with each other about how you feel and what you want. From the beginning I would've said she wanted you to be there but mightve met some new people or felt a desire to experience some things that were a little more taboo (outside of your relationship). Sounds to me like she might've been doing that. I probably wouldve asked her why she lied and talked about it with her.
The whole finals crap is stupid, unless she always acted like that, the chances are its not just about grades. Sounds to me like she may have been considering taking a step away from the relationship to see what it feels like, which tells me one thing about you guys as a couple. Either, you're way too close all the time, or, you aren't in love but you like the idea of it. Towards the end you made a series of not very well-thought-out moves to determine her feelings, but I don't think you were prepared to do half the things you acted as if you were, nor do I think you were prepared to give this up in the slightest.
However, I do not know your relationship with her. All I can say is, I wish you hadn't dove back in so quick, I think she realized you might be slipping away and grabbed you as quickly as she could. Chances are she's not going to stop whatever she's doing, she's just going to find another way of doing it... or... it'll wait a while, and then come back out the same way it did now. If you're going to stay with her id seriously consider not allowing yourself to be too attatched because I don't think you or her have any idea where this relationship is going, you are acting based on a feeling or a multitude. Relationships are about communication, trust, respect, love etc. not attachment or telling each other you love them in a cute way. Make sure you really think about what's going on dude, don't be a fool, don't go overboard, but don't get played and don't play her. All that you will get is some pretty crucial pain in the end if you do. Take my advice, been there, done that... twice! 2 years a piece, sucks. Im still getting over one now, and believe me, it couldve gone on, I just finally realized to accept the things in the back of my mind that I knew were true and step away from the safety blanket. Good luck to you my friend, and please, if you ever want to talk about it I'm more than down, I check this about every day.