Life Bite Series. Loneliness can be very debilitating. You can feel lonely right in the middle of a bunch of friends and family that love you. You don't have to isolated to be lonely. However the most common cause of loneliness is a degree of selfishness, a selfishness that thinks of oneself more than sharing with others.
It can even become habitual and self consuming so that one lives in a bubble of "all about me" and then starts to feel that "I can't be bothered" or "it will be late" or "An excuse here" and so on. Unless you live in the middle of nowhere or are infirm then there is no excuse to be lonely other that the actions you take yourself to make it so.
You can always phone people and if you ever say to yourself "I phoned them last time" then you have just shot yourself in the foot by announcing what a narrow cheapskate you really are.