To date, I have had trouble being left alone and not having someone to lean on when I need it, but I have been discussing some recommendations from experienced people.
The first step is trying to make time alone be quality time with yourself, this think can help you to don't fell alone because you have you. Before find joy, because you need to try feel happy all the time, to forget the bad things (I try to do, and it work). Then be a good neighbor and phone a friend, to have someone to support you with when you need it. Little by little talk to a stranger because you can have new friends.
I do not promise that it works for everyone since we are different, but it does not hurt to try.