My experience with depression is that it does what it can to feed itself. Whatever triggers it (for me I am certain it is brain chemistry) doesn't really matter.
Depressed people detach socially from their support network because that feeds the depression, and any plausible explanation feels as true as any law of physics. All you have to do is pick one: "These people don't care about me/They can never understand/They are better off without me as I will just hurt them."
One way I describe depression is that it's a detachment from reality. Whatever reality you are actually in, depression bends and warps it to such a degree that mentally healthy people could not understand even when described to them.
I can vouch for this. I had a small group of close friends, who all seemed to tolerate the fact that it doesn't naturally occur to me to pick up the phone, invite them over etc. But after 2 years of serious depression, they've all drifted away from me. I don't blame them: I imagine it just becomes untenable to keep trying with someone who doesn't answer their phone, or never replies to your messages...
Not in my case. I have family and friends close by. I'm convinced it's something wrong with the chemical levels and receptors and in the brain, something that pharmaceuticals can help with. It doesn't have to be standard pharma: I'm reading encouraging reports about Kratom, LSD microdoses, Ketamine, and Psilocybin (Mushrooms.) I take Abilify which works wonders for me to keep the Black Dog away. Now that they off-patent (or something, I don't really understand it) it's cheaper. My initial look at it was going to cost around $900 a month so I could not continue even though it worked, so I suffered for another 2 years before I crashed. Now it's cheaper and working fine.
I think it works the other way around, it causes detachment. Which doesn't help, sure, it may become a new source of despair. But getting rid of that one source won't change a thing, there are plenty of others.
I am fortunate in that I don't really suffer anymore; as I was "getting better" one thing I came to embrace was how little sense it made. For awhile I kept a journal, and if I read the entries from the bad times aloud, I'd be constantly apologizing for them and admitting that the feelings didn't make any sense. I intellectually understood the meanings of the words, but the emotions behind them felt foreign. I mean, I remembered feeling that way, but I couldn't understand why. As things improved, I was able to get to a place where I could just resign myself to being hopeless for no real reason, but with the understanding that, in my case, it would fade on its own.
That wasn't the "fix", but just an interesting step along the way.
Depression probably isn't a single illness, and most forms probably don't have a single cause but are a complex mix of "bio psycho social" stuff that reinforce each other.
