Blien,
I just wanted to say that I think you've made a wise choice in deciding to not move in with this girl. As others here have pointed out, it would be problematic in many ways. When it is the right time for you to move out, God will open the door and make His path clear to you. Stay close to Him in prayer and ask that He reveal His will to you.
I'm sorry that you're not in the greatest of living situations right now. I understand completely, as I grew up in a less than desirable household... Aside from living in a dorm when I went to college, I lived with my parents until I was 25. I was so sick of it and wanted a way out, but nothing was working out and my budget seemed to tight to make it work. When I gave it all over to God, though, and stopped seeking out solutions on my own, God literally just dropped the perfect living situation into my lap-- a whole new life, actually-- new job, new friends, etc.! He sees all that is going on in your life and will deliver you in His perfect timing.