I thought this was a fine twist-ending oneshot. The problem (for me, anyway) with this sort of thing as a longer series is that, unless the writer wants to flip the tone from creepy to fluffy, they’d need to keep upping the dysfunctional ante, and horrifying romance just isn’t my cup of tea.
As to this being unrealistic, I tend to see stories like this as the psychological equivalent of science fiction (without the science)—a kind of ‘what if’ or ‘imagine that’ rather than an attempt to depict how a real-life situation would work.