! The infamous "Was Bisexual, Now Monogamous" line
In ''Barrayar'', during a social event one of Aral's political enemies tells Cordelia about rumors that Aral was bisexual. Not realizing that in homophobic Barrayar, this man was trying to torpedo Aral and Cordelia's marriage, Cordelia glibly responds that Aral "was bisexual, now monogamous" - a deliberate display of ValuesDissonance between Barrayar and Cordelia's home of Beta Colony, which has also earned at least a few notes around this wiki as having some UnfortunateImplications.
One forgets that Beta isn't a stand-in for the present-day United States (or even California) any more than Barrayar is properly a stand-in for present-day Russia. Each takes and exaggerates elements from these societies, but is not wholly informed by them. In short, it's also meant to be a deliberate ValuesDissonance between Beta and Bujold's target market of present-day English-speaking ScienceFiction fans.
It's less obvious because we get far fewer direct glimpses into Betan life, but what we do see shows that Betan society is heavily "psychologized," so to speak - they have an almost obsessive tendency to psychoanalyze and deconstruct their understanding of themselves and other people. As such, the Betan understanding of sexuality takes a distinctly different turn from how most modern Western societies understand it. To wit, for Betans, sexuality is not about an "orientation" but about practice - your sexuality is described by ''what you do''. As such, it is something that can change through one's lifetime as one's own sexual practices change. If a Betan man was to go from exclusively having sex with other men to exclusively having sex with women, then he would have been "gay" for a time, and then "straight" (and would be "bisexual" only if such practices overlapped for a time, or in trying to sum up his whole life's sexual practices in one word). If one was to frame it in modern Western terms, then it would be said that many Betans have a fairly fluid sexual orientation that shifts across their lifetime. (Betans wouldn't say that because, again, they would say your practices were what's fluid, and that "orientation" is an artifact of a restrictive understanding of sexuality that relies on categorization and fitting people into boxes. Kinsey has nothing on Beta.)
Monogamy in Betan society thus itself becomes a form of sexuality because it describes someone engaging in an exclusive sexual relationship, which is not universal given Beta is something of a FreeLoveFuture. Monogamy is about deliberately choosing to practice a SingleTargetSexuality. As a result, in the Betan understanding Aral Vorkosigan would be said to have at one time practiced bisexuality (as he had a wife and also at least one male lover at the same time) and then began practicing monogamy when he took up with Cordelia.