It's not the HUGE, great big nasty things people like this awful girlfrend do that hurt those in their lives the most actually, its the teeny weenie things. The nail thing is SO heinous!
You have 2 weeks before you move, you need to tell her now that you will be moving, and she will not.
Next, you will get some help (from here perhaps) to rebuild your self esteem to never ever, EVER get yourself so deep into such a bloody awful relationship.
She is no princess. A princess would not be so vile and mean to her own kids. That poor little girl was not upset, only a bit disappointed, because she is already accostumed to being put way down at the bottom of this awful woman's priorities.
She's no mother. A real mother would feed her kids before she eats. She is no woman, no partner, no girlfriend. A real woman wouldn't allow you to get yourself into hot water money wise on her account.
It looks like she has screwed up her own credit, and is on the way to screwing up yours too.
You do know what you need to do. It will be easier once its done. You can always be there for her kids if you want to be, but you have to get yourself out of this asap.