Good Morning ...... This usually happens after a break-up/separation causing stress leading to certain adjustment issues. Currently as ur question is not well described with that one fear of being alone its seems to more of Anxiety spectrum. First of all take a break be out with family or frenz whom u can rely  n ventilate about the break up ........ Have adequate sleep ......Try doing some relaxation exercises ....... If u have tried n was not able to overcome ..... Please consult ur Nearby Psychiatrist or Psychologist and reach out for help Wishing you a Speedy Recovery Regards, Vinoth Krishna Dass