Fear of being alone, losing everyone i care about.
Not much can be done to beat it. Im the youngest male in my family. Eventually everyone i know WILL die before me, assuming of course i dont have any kind of accident or get murdered.
The only logical course of action is to ensure i can children, to prevent exactly this. But therin lies the paradox as i dont want children. Thus my only course of action left is to accept and face reality.