This is especially weird given that the game that inspired large parts of Rimworld, Dwarf Fortress, is actually really good about this. Dwarves can belong to one of two sexes, male or female. Each dwarf can receive one of three possible reactions to a given sex - they can be disinterested / interested, but not in commitment / interested in commitment (the former will take lovers but not marry, the latter will attempt to marry partners). If you ignore for a moment the difference between the commitment levels, that allows for four basic sexual attractions: straight, bisexual, homosexual, asexual. Both male and female dwarves are equally likely to end up in any of those four categories (and both have even stances on commitment).
It's not perfect - it does dichotomize a fluid range of possibilities into four discrete categories. But as an abstraction of something enormously complex, it does an excellent job, and I've had various different dwarven couples that I've been pretty strongly attached to as a result of the level of depth that goes into the relationship mechanics. It's pretty common for players to do generation games, where they attempt to create dynasties of the original dwarves, just to see how the families progress and how the relationships form.