Hi, @Angeleek. Thanks for raising this topic. It is something I think about a lot. Like you, I'm not a medical expert, just a recovering nicotine addict who is trying to make sense of my own personal experience. It's especially helpful to hear you talk about your experience of no-man's land.
With something as complex as depression, I'm not sure what I think about causal factors. But I can say with certainty that smoking damaged my mental health. I'm still puzzling on this, but some things I am beginning to understand:
I believe that smoking diminished my ability to experience pleasure. My brain became trained on one thing: getting a nicotine fix. Other experiences faded into grey, and my ability to feel joy receded... as if my nicotine receptors had cannibalized everything else. There is some science to support this theory, though researchers are still trying to understand exactly how long-term nicotine exposure disrupts production/uptake of dopamine and other neurotransmitters associated with pleasure and contentment.
Smoking undermined my sense of self-efficacy. Being in thrall to nicotine (or any other addiction) is degrading and dehumanizing. That affected me more profoundly than I realized.
I used nicotine to try and suppress negative emotions, like sadness and anger and grief. Such feelings (and their underlying issues) weren't cured by smoking, of course. Smoking just blunted them. Rather than addressing the root causes of my distress, I was pretending to "soothe" myself while feeding myself poison and ducking my own feelings. Naturally, this kind of self-betrayal was another negative force on my mental health.
For me, stopping smoking did not automatically resolve these issues. I did not experience the quitting euphoria that some other people describe. And there's still a lot to untangle about why I smoked in the first place and what my baseline mental health is. Like you, Angeleek, I started smoking really young. I was hooked by age 13, so I don't really know what I'm like without nicotine. For people who got hooked when our brains were still developing, are the effects different? I don't know.
But I certainly DO know that the psychological damage that smoking caused was real, and that quitting is the only way to heal the parts of me that were injured by it. Whatever else is present on my internal obstacle course, quitting will simplify it. And since I quit, repair is happening. My progress is slow and herky-jerky, but I am starting to cope better with my feelings, beginning to see glimmers of light and joy breaking through. Quitting will make every other good thing possible.