My partner also left me, partly due to my depression. I was so deep in my own hole that I couldn't see how I was dragging her down. She also has been depressive in the past, so she knew that she couldn't "fix" me and that I had to take some steps myself. I wasn't, and it finally got to be too much for her. She did the healthy thing and left.

I have to remind myself that she actually did this out of a place of deep caring and genuine concern. Just remembering that has given me some strength to continue, and I've stopped beating myself up every day over losing her. I'm still intensely sad about it sometimes, but I'm trying to use the experience to become a better person. I hope you can, too.