I used to think the same thing you did, and then I woke up. The fact is, he’s not undeserving just because he left me for me being depressed. He came back, right? He just needed a break. Everyone has a breaking point.
Also, my depression is really horrible. He told me all the time of how he felt helpless because he’d try to cheer me up and then see a post on tumblr made by me telling myself to “kill yourself already.”
I told him the same thing, “writing on tumblr is my way of venting” “cutting makes the pain inside go away”. And maybe he didn’t understand, but ever since I stopped both of those things for him, I have been so much better off. The “venting” did not make anything better. Writing notes to myself to remind myself I’m “worthless” and “deserve to die” did NOT make anything better. I do not need to vent to anyone, because I’m fine.