I really didn't want to comment on this because I didn't want to bump it but I want to give you some advice.
If you have the amazing blessing of being able to live with people who not only love you, but your child, in a time where you are obviously still a child yourself why would you want to move out? I'm assuming that you've never lived on your own before, due to your age, but let me tell you as someone who tried to make the jump of moving out too quickly. I moved out of my home at 17 to get my own place and was in SHOCK of how expensive living was. I honestly couldn't imagine doing it with a baby, while not working. It's foolish to think that anyone anywhere could get by with 2 people going to school fulltime and working full time with a new baby. Diapers, childcare, health insurance, formula, plus your tuition, your rent, your utilities, your food, your transportation. It doesn't add up.
Obviously I don't know you or your girlfriend. But don't get married for the tax refund
... that is the worst advice I've ever read on a forum, ever. Marriage is no joke and at 19, even though you have a child together, neither of you are now who you one day will be and I never would suggest anyone get married that young.
Stay with the grandparents, go to school, make something of yourself, if you and your girlfriend make it through school and still love each other, then get a place and get married and save for your childs college education.