Separation after 9 year relationship due too depression?

I was in a 9 year relationship that ended 2 months ago. My GF has been suffering from depression for about a year prior to the breakup and started to see a therapist. Soon after she came home one day out of the blue and told me that she was moving out, and that she needed to be alone. There has never been any infidelity on either part and we had a perfect relationship, not even any terrible fights to speak of. We were and still are best friends, and we have seen eachother a few times since the split. She says that she still loves me and its nothing I did, that its her state of mind that is to blame for the separation, but I don't want it to be over, I still have very strong feelings for her, I was ready to spend the rest of my life with this woman. What can I do to convince her that we can overcome this together and that being alone is the worst thing you can do for depression. I would appreciate any advice. This is tearing me apart on the inside. 9 years of devotion is worth saving!