I should of kissed her right?... What do you think?

You did the right thing by not act on it, because she is still into her ex girlfriend. Even if she gave you a chance, subconsciously, you would feel unsecured or might think that she is using you.- there are abundance of unpredictable thinkings that one might think of in situation like yours. However, you should have confessed your feeling before she leaves. it will give you an emotionally and physiologically released as a self closure.