system
A chat on subreddit /r/NoStupidQuestions
human
I think it is deeper than that. It goes beyond the fear of being dumped for another (because that can happen even if they aren't bi-sexual). I think it is the fear that the reason they will be dumped is because the person they are with has desires that they can never directly fulfill. I'd imagine a short petite woman would have a chance of feeling a bit insecure if they found out their boyfriend is also really into tall buff Amazonian women.
gpt
&gt;because the person they are with has desires that they can never directly fulfill.

I've never really understood this idea either. Even people who are attracted to a single sex can be attracted to a wide variety of people. I would never assume that I alone would fit all the desires of someone, even if heterosexual.

A woman can be into both dad bod and bodybuilder types, a man can like both short and tall women, etc.