I don't think she's actually going back and forth; she knows that she's Gi Hyun's weakness and the reason why he's always fighting off demons and weakening, so I think she wanted to leave so Gi Hyun wouldn't have to keep getting hurt for her sake
I only understand that she wanted to protect Gi Hyun all along. Story may come off confusing but there was something there that made her leave and come back. Regardless of that, Gi Hyun himself knew she would to and waited for her. In the end, they both truly loved each other; just some things didn't go how they wanted.
That human guy is so annoying and so is the doll. She keeps going back and forth. Gi hyun deserves so much better. And that fox lady is suited for that lip piercing guy yup they're both shrewd