Hey, I've firmed Manchester for 2012 entry Medicine too! :-)
Are you a school leaver or a grad/mature applicant?
I see the attraction having been in a long-term relationship myself, but if you are a school leaver I would advise against it as you don't want to be out of the loop after one year when your girlfriend has moved to Bristol or, as you said, if it doesn't work out.
I don't mean to be negative but this is a new chapter in your life and I just don't feel you'd fully experience it living out of halls :-)