Loneliness and aloneness are not so much about the other; they are about the relationship you have with yourself. If you have been living a life that your best self, that your internal honesty cannot approve of, then you will be very lonely. Your relationship with yourself would be fraught with contempt and disgust.
It is not a nice situation to be in—in which you are contemptuous of yourself, right? You know what you have been doing; you know that better than anybody else. You know the kind of life you have been living. You know that you cannot respect yourself. That is loneliness.
When you cannot like yourself, then obviously you have to turn to somebody else. That is loneliness.