People do strange things when they are scared. I can understand how a closeted man or woman can lead a life that would keep questions at bay, but getting married is taking it to an extreme. As for a bi person who is married or in a relationship somehow Needing to have sex with alternating genders or else their genitals will wither and die, no i don't buy that.
People will do what they want, some might look for a pass from strangers on line but most will just do what/who the fuck they want when they want and not give a damn about a partner, who becomes more of an inconvenience or trophy/mask.
You only have to answer to yourself at the end of the day, but it does not take much effort to take other people into consideration.