Grace, I'm sorry about your situation. I'm not the most experienced person here by any means, but I've been separated twice so I'll give you my advice.
I really can relate to something you said, that once they move out, they are gone forever. This is not true. I know it's scary to let go, but you are not getting anywhere with your situation living together. My opinion is that he needs to miss you to be able to make a change. Don't be scared, GAL, and do things that you like to do. Really, truly focus on yourself. I also consider myself a people fixer, and let me tell you, when you truly let go and let the other person handle their issues, it is such a relief. I've come to the conclusion that there is NOTHING I can do to influence or change a person. The change has to come from them. Good luck and we are here to support you