Take as much as time as you need to process that she's passed on and liek Bishopu said, try to reach out to other people in the meantime so that you're not alone. Much as that may be difficult to do. The last time I lost a loved one was when I was so young I couldn't understand it properly. If it's any consolation, I can't remember much about my grandma from as a child, but you as an adult can remember much more about your girlfriend. Try to think of those memories you created together in stride, not in grief.