"Can [Psychopaths] Feel Loneliness? If it is loneliness, what is Loneliness to you? Is it Emptiness, or Boredom, or Restlessness, ...?"
I Can't speak for other psychopaths, really, because I've never discussed the subject with anybody I knew to be psychopaths. The topic just never came up, and I think the reason for this is very likely that to most psychopaths the concept of Loneliness isn't part of how we think and how we perceive life and situations, so it isn't really 'real' and doesn't figure as part of most psychopaths' past experiences. And in the cases where it does, it doesn't seem important or memorable enough to the individual for them to bring it up or think about it.
For me personally, I don't think I can feel Loneliness. I've never felt lonely, not even when I was in solitary confinement in prison, and that lasted for several years. So I don't think I can answer the question about what loneliness is to me, because it doesn't really exist to me. But being alone for extended lengths of time can lead to boredom, and that leads to restlessness and eventually frustration and even anger. But it's got nothing to do with feeling loneliness, it is not about feeling or not feeling loneliness. It is about not getting the stimulation you need, not having any means or sources of fun, nothing interesting to explore - like f.x. people. To me other people can be very interesting as well as fun.
"[Is it] some other Unbearable Feeling you can't quite distinguish, or some itch you can't scratch, that keeps you on the move, keeps you searching, always? Is it feeling...forlorn?
My need for stimulation is the only emotion that can at times feel unbearable, which happens in situations where I am physically unable to take necessary action and find a way to satisfy the need, such as during some periods under imprisonment. But my need for stimulation, or being cut off from seeking gratification, has nothing to do with feeling Forlorn. There is no sense of having been abandoned or of being lonely.
When an urge to go and seek out stimulation or excitement comes over me, I don't feel forlorn, and where company is concerned it is far more often me who leave others than it is others who leave me. When I leave somebody or someone, it is usually because I feel my needs are no longer being met, and more often than not it is my need for stimulation that is no longer being fulfilled - though it can also be other kinds of needs, f.x. in the form of knowledge that somebody could and did provide until the supply ran dry. While I was in my teens there would sometimes be monetary needs.
To the majority of psychopaths, myself included, it is all about having a good time, feeling excitement and feeling good. 'Feeling good' often relates to feeling in control and feeling able to 'run' other peoples' lives, but again feeling forlorn doesn't enter the equation.
But where I differ from most people - though of course there are others like me - is in that for me to feel satisfied I need to feel I have learned something or am learning from whatever experience I am having. Stagnation is the ultimate deadly toxic, both in terms of how I experience things and in terms of how I think and understand reality as a whole. I really have a wish to grow and evolve, to become stronger and better at being me, at being who I am and who I am going to become in the future.
I constantly aim to find the best way to function, a way that will generate the highest possible degree of satisfaction and gratification in every sense of the word. And it is this, I believe, which has brought me to eventually study the possibility of turning cooperating with my surroundings into something that can bring me new experiences that are at least as exciting as what I've experienced in the past. Being useful, helpful to others and contributing to society in some form or other, is part of the plan that will hopefully lead to that result. It is not because I have become less selfish than I always was, but I may be smarter.
Still, nothing of what I have described has anything to do with being or feeling forlorn. People will still come and go in and out of my life, and I will still feel fine about it just as I have always done. I do on occasion - though rarely - feel a certain connection with somebody I get to know, but I don't feel forlorn when and if I leave them, or if they leave me.
So at the end of the day I still cannot describe what loneliness is to me, because I have never felt it. Apparently it isn't part of my reality or life experience.