Am I on the rebound or rebound relationships?

No, it doesn't sound like it is. Rebound means you go to be with someone else just because you don't want to be alone and still aren't over the other relationship. That's not the case with this new guy. You did wrong by sleeping with him when you were with someone else but you did the right thing when you broke up with your ex. It sounds like you are getting along will with this new guy and have like him for awhile, have fun and be happy.