It depends on the nature of the interest. If it's just about exploring different relationship dynamics in fictional stories in a respectful and non - exploitative way, it can be considered ethical. But if it involves objectifying or disrespecting real - life relationships, then it's not ethical.
Ethical considerations are complex. On one hand, if these stories are about consensual relationship models that are being presented in a positive, non - judgmental way, and the viewer/reader approaches them with an open and respectful mind, it can be okay. But if there is any form of misogyny, non - consensual behavior promotion, or objectification in the stories, and the interest is in those negative aspects, then it's clearly unethical.
If the interest is purely from a literary or fictional exploration perspective, where one is simply reading or watching stories as a form of entertainment and not causing harm or disrespect to others, it can be ethical. However, it becomes unethical when it crosses the line into inappropriate or non - consensual behavior. For example, if it promotes the idea of cheating without consequences or disrespects the privacy and rights of others in relationships.