You said it yourself, you have no one to talk to, and feel lonely, this is why you miss them. You don’t actually miss that person, you miss having company. It would be foolish to go back to having a toxic person in your life. You need to make/meet new friends.

If they were toxic, it’s good they are out of your life. We sometimes hold on to people that are bad for us just to keep from being alone

Don't look back. Eventually, you'll meet more people.
Population is exploding, you know. So, just relax.

I feel you on this.

Karma sucks.. i got my fair share to deal with.