Bisexual folks don’t end up in other-gender relationships a lot because they’re ‘not really bisexual’. It’s just that, statistically, most people are straight and therefore they’re more likely to meet someone compatible that is of another gender.
Please support bisexual folks when they end up in other-gender relationships. They are still same-gender attracted. They are still the same people. They still feel hurt when people call same-gender attraction a mental illness, immoral or disgusting. They still face their parents, friends and family not fully accepting the real them. It’s just than now they also have to contend with a bunch of the queer community also not accepting them.