All the advice on this thread so far is great.
I'll just add my own 2 cents
:
Enroll your new pup, you, and your girlfriend in a "Doggy Kindergarten" or Beginner Obedience Class. It sounds like you two and your pup have a lot to learn about and adjust toward each other. These classes are not just to teach "sit" and "stay." More importantly, they also provide valuable instruction and support to new dog owners on how to interact and socialize with their dog(s) and maintain a healthy and structured relationship with each other. Well-behaved dog
and owner = happy dog and owner.
Build a strong relationship with your veterinarian. You can always call them with any "new dog" questions; they are obviously your best resource for medical advice, and can also refer you to a certified veterinary behaviorist should the need ever arise.
Good luck and have lots o' fun with your new pup!