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...
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.