Monster

I think this is similar to your last question about Desiree's Baby. John is a patriarchal unfeeling jerk but sadly reflective of many men at the time. The problem with the word "monster" is that our modern context does not necessarily fit with the Victorian era. It is possible that John did not intend on doing harm to the narrator. John is a reflection of patriarchal control that often crossed the line into misogyny, The fact that John actually thought this "rest cure" was in the narrator's best interests might save him from the term "monster".