Lies are the language of modern society, while you and her should be able to be 100% honest 100% of the time the fact of the matter is unless y'alls relationship is 100/100 best of the best, and you're a special type of couple and individuals, then NEITHER of y'all want the truth most of the time.

Learning this language, while it is relatively psychopathic as you put it, is a must, but in some cases like now you speak it so fluently it just comes naturally and you're compelled to not say anything as you feel wrong you didn't before.
Give it a night or two, and when you have a week left be ready to tell her and have a plan of some sort, even if it's sub-par, of what you'll do to potentially mention to her to reassure her, especially if you have financial problems, although I feel as if that's unlikely.