It may be a lot to ask but why can't the girlfriend move to accommodate you getting the degree? A good education cost a lot; you'll be getting it for free and be receiving a salary. Sometimes we have to make sacrifices to get the finer things we desire. I will not allow anyone get in my way of getting a good education, especially if I don't have to pay for it. Eight years will go by in no time.
Suppose something happens between you and girlfriend causing you all to go your separate ways, you'll regret passing up this opportunity for the rest of your life. I hope you make the right choice. All the best to you.