I think the difference is the perceived energy barrier if one wanted to fool around on their partner if they a bi vs het.

A bi guy could, hypothetically, find a guy on grindr pretty much on a whim if he wanted to. This is a much lower barrier than straight guys face unless they seek a sex worker. If you are a woman in the early stages of dating someone, where you don't know yet how much you can trust a guy, if a guy tells you he is bi that can come off as a higher cheating risk than a straight guy.

Straight guys dating a bi-girl don't have a similar perceived risk increase. Early in the relationship, guys may not even see the potential of a bi-girl hooking up with a girl as 'cheating', vs a bonus for his enjoyment. But also - finding a new girl to date is considered harder than finding an interested guy. So the 'cheating' risk doesn't feel that much higher for guys dating a bi-girl compared to a straight girl; he may feel like he is still mostly competing against other guys.

Is this fair or even realistic? No, this is based on perceived stereotypes rather than the behaviors and character of individuals.

But this plays out at a stage of dating where people don't know each other well yet and are relying on heuristics.

Um, no. I am an old Xer lady and we know men can be bi too. And like the ladies... sexuality is on a continuum. Some people just love to canoodle with young beautiful bodies no matter what flavor... and as we get older, old beautiful kind considerate people.

Bi men here, progressive women are not like that. Only "progressive" (read: plays lip service to some popular cause, until it's popular, often are TERFs etc.) do that, and you just need to skip on them, for more than one reason. I almost dated one, she turned out to be a "progressive" anti-abortionist, because "babies are people too", and "you can just use contraception".

Women will leave him? I'm surprised to hear this.

Jim Jeffries talked about this topic in his new Netflix special that came out last week.

Just shows how deeply ingrained power relations are in society with an unproportional low complementing awareness and reflection about it.

If he's a hot twink, then yeah no that'd be fine with me. Perfectly understandable.

Heteropatriarchal system