This is making me think of something one of my bi female friends complained about. She identifies as bi, but I've known her to mostly have female partners.
She says she is up front about everything when she has a steady female partner in her life, but that most guys she sees doesn't think her relationship with a female can possibly be a serious one. They tend to think she is just playing at the bi part and once her emotions get involved, she will just naturally gravitate to a mono relationship with the guy. Or that he will get to be with them both with he and her taking a front role and her female partner as an aside.