I think you're right. It probably is a lot of depression but I understand what you're saying. I was in the same situation a year ago.
I was depressed at the time and losing the friendship really sent me off the edge. We were friends for 34 years but she just couldn't handle the craziness of the BP.
One day she was texting me then she just stopped and wouldn't reply to my texts or answer her phone. Never did find out what the deal was.
Slowly the depression started to lift, I was busy with therapy, groups and trying to put my life back together.
I won't lie, It still hurts to this day and I think of it everyday but life has to go on. I truly believe that people come into our lives for a reason then they leave. There's a lesson here to be learned, you just have to figure out what that is.
I also wanted to say that you need to prove to yourself that you can manage without her not the other way around.
It really sucks but that's life I guess. I have no words of wisdom really, I still hurt.