Much of what is spoken and written on this issue might well be well meaning, well intentioned, but it is also twaddle best found within a fortune cookie.
One way of thinking about it is to consider that a human is just a shell, a container for the interaction of chemical and electrical impulses. Via the intricate cabling system we call the nervous system your body responds to the stimulation produced by the aforementioned. You can call it many other things, feelings, emotions, sensations whatever you like really. What we know is all humans need stimulation. Without stimulation you are a sick puppy and at an extreme you are dead. However, not all stimulation is created equally. Your body will register some stimulation positively and some negatively. It should go without saying this varies widely individual to individual in the main dependent upon prior learned experiences. Let's just lump that lot and call it conditioning. In a dream world we would test any given individual to find what experiences create for them a point of stimulation equilibrium where the stimulation they receive leads them to be mentally stable and physically productive because of it. By playing around with tests we might find find which stimulation is putting them out of equilibrium. That is, mentally struggling and consequently physically unproductive. If in the main you think you are content, happy etc then take a bow as you have a balance of stimulation that is right for you. A psychiatrist looking at the person who is not content etc might focus on the chemical side of explaining that and try to correct it with medication IF diagnostically that appears to be the crux of the issue. A psychologist in the main want to look at your life, your relationships, experiences and try to identify that stimulation bugger that is putting you out of balance. Unsurprisingly, the latter is all too oft relationships that are creating negative stimulation. You are sad, depressed, unhappy, but 'stuck'. I am sure my daughter would agree wholeheartedly with me when I say many people can be mentally improved just by either cutting ,or changing a relationship(s). It's important to understand this is not about talking you better. It is about behavioural diagnosis and taking physical actions based upon that. You can't talk somebody into being happy ,or content. To get there something in their current lifestyle has to change!
That's why I applaud our friend above. Whatever his situation now it appears clear that it is improved because he found the motivation to 'cut' a relationship that was not working positively for him. Too oft people are conflicted on this ,because they fear the change more than they fear their current state of 'happiness'.
Lot of simplification above, but I doubt anyone wants to read a 'War and Peace' version.