My advice is do not move in with your girlfriend in first year. There's no rush. I know lots of people who didn't live in halls in first year and they ended up feeling isolated. I know you can socialise in your breaks but it's not the same. Halls are a totally different experience which you may or may not like, but uni is all about experiences and trying new things.
Also many couples choose to live together. A lot of them break up. Can you imagine how awkward that is?! I'm sure things with your girlfriend are great but there's guarantee there'll stay great. If you break up or go through a rough patch, there's no escaping her. You're in your first year of uni and I'm not saying you'l deliberately do anything but things happen, you change as you become more grown up and independent so your relationship will likely be tested. No reason it can't last through uni, just don't get yourself into this little 'perfect relationship' bubble, give some thought to realities. I also think it's important to have a separate life, not just be a couple. You have loads of time to see where the relationship goes and move in together when you're in second year or after you've graduated.