There are various reasons. She may have had a change in her life situation. For instance, if she has been through some tough times recently, she might be longing for the security that her old boyfriend used to provide. Or perhaps she has grown as a person and believes that they can now handle the issues that led to their breakup in the past more effectively. Another aspect could be the influence of mutual friends or family who might have encouraged her to give the relationship another chance.
She might go back to her old boyfriend because of familiarity. They already know each other well, and she may miss the comfort of that old relationship. Maybe they had some great memories together that she can't forget.
One reason could be for medical issues. For example, if she has a bladder or bowel problem that makes it difficult to control her functions. Another possibility is psychological stress. Maybe she's going through a tough time and unconsciously reverts to a more infantile state for comfort. It could also be part of a role - playing or regression therapy in some cases.
One possible reason could be the bgirl's strong influence on her boyfriend's sense of style. She might have a great taste in fashion and the boyfriend was intrigued by it.
Perhaps there are emotional undertones that she's not fully aware of. Maybe she has feelings for the other person on a deeper level, which is expressed through the physical act in the story.
She could meet her younger self. This would be an interesting encounter as she could offer advice and guidance to her younger version. Maybe she could help her younger self to be less afraid of her powers.
She might keep coming back because she has unfinished business. Maybe there are unresolved emotions or issues in the relationship or situation described in the story.
One possible plot could be that Harry is sent to Hell due to a powerful dark magic spell gone wrong. In Hell, he has to face his worst fears and demons, both literal and metaphorical. He might encounter lost souls who tell him secrets about the magical world. Eventually, he manages to find a way back, using his wits and some unexpected magical abilities he discovers during his ordeal.
It could also be that she is so focused on spending time with her boyfriend that she ignores her body's needs. She might be having such a great time with him that she doesn't want to take a break to go to the toilet. Or perhaps she has some insecurities about her body functions and wants to keep them private from her boyfriend at all costs.
Maybe she has an irresistible charm. It could be her personality, like she's very kind, understanding and full of positive energy that makes him feel really good around her.
In some fictional stories, it could be due to a lack of emotional connection in her marriage. Maybe she feels neglected by her husband and is seeking a form of intimacy elsewhere. Another reason could be a form of rebellion against the constraints of marriage.