Anecdotally, I lost multiple male friends when I came out as bisexual, so the “fragile masculinity” theory feels especially apt. The fear of being perceived as anything other than heterosexual by association seems to be a big problem with many men.
"only a great fool would reach for what he was given. I am not a great fool, so I can clearly not choose the wine in front of you. But you must have known I was not a great fool; you would have counted on it, so I can clearly not choose the wine in front of me."