That's a very good question!
I haven't felt really alone in a long time.
It happens that for a couple of minutes it seems to me that I was left. But, as a rule, it is connected with some specific person, and as soon as the relationship with him changes, the world changes, and I become happy.

In principle, I can say that seriously I do not feel lonely, because I know that I am always connected with everyone. And it depends only on me whether to meet the world.
And around there will always be those who need you, who will rejoice you. So loneliness is a big illusion of the mind. I think so.