Sorry to hear that. I understand what you mean. I know people that have friends since childhood. I wish I have one but friends leave sometimes and we can't do anything.
You have to be sure that you are your best friend in life so you have to love yourself first of all to be able to love another people.
When I feel alone, I use to go for a city walk. See another persons around me make me feel that I am not alone I the world and there is a chance of introduce new friends.
Hope you find all what you need. You are not alone in all of this.
Lot of hugs