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
And there is some truth in this. A small amount! Not enough to make me dump someone but……..when I’m with a woman I miss the penis and when I’m with a man I miss the boobs. I deal with this by imagining the thing I’m missing when I’m doing my own thing and appreciating what I do have when I’m doing my partner.