Loneliness, I think is yet another subjective construct that we insist on imposing objective definitions. All we know from the latest neuroscience is that it’s just another variant of basic affective displeasure (emotional pain). Each individual constructs this emotion by adding their context, concept and past experiences to the experience of emotional pain.
The Problem with emotional granularity is that if you misdiagnose the emotion, you then proceed to mis-prescribe an antidote. For example diagnosing what may well be depression, boredom or even hunger as loneliness may lead you to then solve for intimacy by seeking a companion.
In my opinion, treating the emotional pain simply as biochemical affect then opens up a plethora of ways to treat including meditation, medication, exercise, diet as well as relationships.
Next time you feel lonely, try a slice of pizza and a glass of chocolate milk 😊