Absolutely it's nobody's business. OTOH, it's everybody's business when any one of us is being marginalized for who they are.
The bisexual is too often treated as the red-headed stepchild of the LGBTQIA community. As you point out, Demeter, bisexuals are more likely to be seen as opportunistic, up-for-anything, and (by implication) insincere in their attractions. People who would go to any length to defend the validity of any other sexual identity or orientation, make exception for the "B" in that string of letters.
Me, I'm just a plain-vanilla cis male boomer, but even I can feel respect for anyone who has the integrity to love whoever they love without regard to gender.