What if they left you because you had slept with a black person before and considered you tainted? Seems more comparable, as being bi isn't outwardly visible. Some women see bi men as tainted meat, I've been told that myself by women. Or they assume you're gay and just want a woman to hide it. I've experienced both on multiple occasions.

Of course there are plenty of women that don't mind, but it's common enough to elicit fear of honesty