How to be alone without being lonely

I don't have a very large social circle and it has gotten even smaller after a nasty falling out with a close friend of mine. I think i'm finding myself latching onto people too easily and then falling apart when they leave my life even if they weren't good for me at all- both in a sense of romantic and platonic relationships. I'm so terrified of being alone and I need to get over it. Does anybody have any advice for how to be alone and enjoy it without feeling lonely? I know that sounds like a bit of an oxymoron but I don't know what to do. I'm not somebody who gets pursued- platonic sense or romantically, so it feels like the better option is to give up on those notions and spend that time by myself rather than hoping for something that realistically will never come and being dependent on those around me.