I am lonely only when I am overtired, when I have worked too long without a break, when for the time being I feel empty and need filling up. And I am lonely sometimes when I come back home after a lecture trip, when I have seen a lot of people and talked a lot, and am full to the brim with experience that needs to be sorted out.
Then for a little while the house feels huge and empty, and I wonder where my self is hiding. It has to be recaptured slowly by watering the plants, perhaps, and looking again at each one as though it were a person, by feeding the two cats, by cooking a meal.