When I was reading about Myers-Briggs-Jung personality types, I saw this trait about Feeling/Thinking. In their concept of personality types, they have four traits: Extravert-Introvert, Sensing-Intuiting, Thinking-Feeling, and Judging-Perceiving.
This Feeling/Thinking trait clicked immediately. I suddenly understood a lot what is happenning to me.
The thing is -- I have been moving from the Feeling type to the Thinking type. And now that I have moved over extremely over to the Thinking side, I have realized that my current depression/sadness is rooted in the demise of my Feeling side.
Feeling was good -- it helped me form relationships with people, it made me have simple minded desires which fueled me onto things. Feeling makes you create a very simple-minded framework of likes-dislikes-desires for yourself, on which you make most of your decisions and choices. You expose this framework to others, and people relate to each other by mixing and matching these frameworks. I think that for being loved, it might almost be "required" to have such a framework.
Whereas "Thinking" is different. You think to make choices, rather than just using some simple emotional framework. I have gone to the extreme end of this line. I think before I even emote. Even the slim emotional framework that still remains in "Thinking" people has become slimmer for me.
This has caused a lot of changes. A lot. Not many of them for the positive.
To live in this world, you need to be atleast slightly tilted towards "feeling", otherwise, you will have a hard time remaining happy and conforming both at the same time. Not that you will understand happiness at that point.
Feeling side is important for relating to people. With no feeling side, it is difficult to have normal emotional relationships with normal people.
[UPDATE: I am orignally an INFP, though converted over time to INTP, but still hold both personalities]