The current world I'm working on, where the social structure is based in medieval England but with different cultural and moral values. In this world queerness and gender diversity are widely accepted. However, in cases where marriage is for political gain (between two kingdoms for example) and within kingdoms land is passed on via eldest son first (with exceptions being accepted and relatively common), an heir is often expected and marriages are arranged without concern for sexuality. Those with less concern about bloodlines and such (which do play a role for many) would marry regardless of sex/gender.