How do I become okay with being alone?

My boyfriend and I broke up a week ago, my friends all have their own lives with uni, other friends etc, and my sister moved cities, got a boyfriend and has a new job. It feels like I have no one now.

I don't have anyone to talk to, anyone to hang out with, anyone to have a laugh with. I'm alone. My ex was a constant, he was always there, always willing to see me...but now although we still talk here and there, I never see him anymore.

My friends barely message me now, rarely even check in to see how I am, it's like they've forgotten about me.

My sister used to be my best friend. Now she's gone. She never texts me anymore.

I don't know what to do. I need something. Someone. Someone to love me, someone to care...