Not all loneliness is the same
Sociologist Robert Weiss distinguished in 1973 between emotional loneliness (missing a close, intimate bond, such as a partner or best friend) and social loneliness (missing a wider network of friends or a group to belong to). Many people also describe existential loneliness: feeling that nobody truly understands them, even when surrounded by others.
Loneliness is very common and affects physical and mental health, to the point that health authorities such as the US Surgeon General have described it as a public health issue. Knowing what kind you feel helps you look for the right kind of connection.