Here's something that people need to remember, and I'll give Elton John as an example here. In 1984, he married German-Australian film maker, Renate Blauel, in a lavish ceremony in Sydney. At the time, he identified as bisexual, but after their divorce, in 1988, he said that he was comfortable being gay. I don't doubt for one minute, and I've read stories of gay men who've married women only to leave them for another man, and read stories of transwomen who were married to women, who, while the women have felt used, have genuinely loved their ex-wives.
And lesbian women who were married to men, who genuinely loved their ex-husbands.
One reason why I think there is biphobia, and I don't agree with it, is that people fear that they will lose their partner to someone of the opposite sex. I remember hearing about a relationship, where a man was bisexual and his wife was heterosexual, and every second weekend, he would go and see his male partner, and his wife would pack his condoms and all. There are relationships where one or both partners is/are bisexual and they live a heteronormative life, but one or two nights every week, they spend the night with a different partner. If there are children involved, sometimes, they say, for example, "Tuesday night, Mum goes off and sees her girlfriend, and stays the night with her, Thursday night, Dad goes and sees his boyfriend and he stays the night with him, and he comes home Friday night, and the weekends are spent with the kids. And I know a woman who is bisexual who is married to a man and her girlfriend lives with them. And they have kids and the kids are well-adjusted kids. Her husband doesn't have sex with his wife AND her girlfriend, some nights a week, she has sex with her husband, and other nights, she has sex with her girlfriend.
How I can best describe it is, my late hairdresser's (one of the first people to suspect I am autistic) father came into her shop one day wearing a Holden cap, yet I'd seen him driving a Ford (Holden is the Australian arm of GM/C) and I said, "That's interesting, he's wearing a Holden cap but I saw him driving a Ford, and she said, "Oh, he's got a Holden AND a Ford." And I knew a man who had a Holden Commodore sedan and a Ford Falcon wagon, and he said he liked the Commodore better, to which I replied, "I knew a guy in the police force who said he liked the Falcon for the comfort and the Commodore for the car." The Queensland Police Force said that typically, they had a 50:50 mix of Commodores and Falcons, but it was 70:30 in favour of Ford, in some cases. Bisexuality doesn't work by saying, "I'm more in favour of one than the other," it's like the man who had a Commodore and a Falcon, or the man who said he liked the Falcon for the comfort and the Commodore for the car. (my joke is, the only Commodore I'll have goes in the CD player." (i.e. a CD with Lionel Richie on it). Each bisexual is an individual.