My sister in law was like that. When I met my wife her sister had a job and was trying to buy a flat. For various reasons she got depressed, cut her job down to part time and moved back with her mum instead of buying the flat. She also said she hated being around people. We tried to get her to see her doctor about it but she wouldn't. Ten years later she's now completely quit her job, has fallen out with her mum but can't afford to move out of the house, so she hardly leaves her bedroom unless she needs the bathroom or the kitchen. I could see it happen as it spiraled into oblivion. I even predicted it at the time.
This is the same situation. Except your girlfriend is using you instead of her mum to support her. You are in a great position that the only commitment to her is jointly renting a property. You've given her seven years of your life and tried to help her for five. If she hasn't tried to improve her situation in those five years then will she ever? Probably not.
You have a decision to make - are you happy with this situation and are you OK with taking on a life long commitment of supporting a depressed adult? Or do you want a life too? You only get one life. You are only young once. Your time being young enough to build a life with someone else fades every day. Before you know it the years will have flashed by, she'll be wanting kids (and then you're doomed, and you'll be much older which makes it harder to meet someone else. You need to make a decision. You deserve a life too. Don't stay with her because of misplaced loyalty or simple habit.
It's a decision i've been contemplating for a while now and is getting more and more likely by the week. I've found out today that she's volunteered at a charity shop that her Mum also volunteers at