“All happiness is of a negative rather than positive nature, and for this reason cannot give lasting satisfaction and gratification, but rather only ever a release from a pain or lack, which must be followed either by a new pain or by languor, empty yearning and boredom.”
— Arthur Schopenhauer, The World as Will and Representation
When someone leaves you once, you expect it to happen again. Eventually you stop getting close enough to people to let them become important to you, because then you don’t notice when they drop off your world.