Firstly I empathise with you. I know how hard it is to 'get your *** in gear' when you are all alone but as you say you are over 18 so you have to start taking responsibility for yourself...though I do appreciate that others should have set the groundwork for you.
Meetup.com is an internet hub that has all sorts of groups so pick a few that interest you. Walking is free ,i'm sure you can join a group. Don't just stay in bed or indoors. Force yourself to go out and start talking to people. Go regularly and you will get to know people and gradually make a few like minded friends. Sure there are a few a##holes but you ditch them and move on . Good luck